Certain 1H-imidazo[4,5-b]pyrazin-2(3H)-ones and 1H-imidazo[4,5-b]pyrazin-2-ols and methods for their use

ABSTRACT

Provided are compounds of Formula I and compounds of Formula II: 
                         
and pharmaceutically acceptable salts thereof, and methods for their use.

This application is a continuation of U.S. patent application Ser. No.12/780,644, filed May 14, 2010 now U.S. Pat. No. 8,299,248, which is acontinuation-in-part of U.S. patent application Ser. No. 12/573,730,filed Oct. 5, 2009, now issued as U.S. Pat. No. 7,956,056, which is acontinuation of U.S. patent application Ser. No. 11/888,902, filed Aug.1, 2007, now issued as U.S. Pat. No. 7,598,248; and claims the benefitof U.S. Provisional Patent Application No. 60/835,272, filed Aug. 2,2006, and U.S. Provisional Patent Application No. 60/921,054, filed Mar.30, 2007; each of which is incorporated herein by reference for allpurposes.

The cytoskeleton of skeletal and cardiac muscle cells is unique comparedto that of all other cells. It consists of a nearly crystalline array ofclosely packed cytoskeletal proteins called the sarcomere. The sarcomereis elegantly organized as an interdigitating array of thin and thickfilaments. The thick filaments are composed of myosin, the motor proteinresponsible for transducing the chemical energy of ATP hydrolysis intoforce and directed movement. The thin filaments are composed of actinmonomers arranged in a helical array. There are four regulatory proteinsbound to the actin filaments, which allows the contraction to bemodulated by calcium ions. An influx of intracellular calcium initiatesmuscle contraction; thick and thin filaments slide past each otherdriven by repetitive interactions of the myosin motor domains with thethin actin filaments.

Myosin is the most extensively studied of all the motor proteins. Of thethirteen distinct classes of myosin in human cells, the myosin-II classis responsible for contraction of skeletal, cardiac, and smooth muscle.This class of myosin is significantly different in amino acidcomposition and in overall structure from myosin in the other twelvedistinct classes. Myosin-II consists of two globular head domains linkedtogether by a long alpha-helical coiled-coiled tail that assembles withother myosin-IIs to form the core of the sarcomere's thick filament. Theglobular heads have a catalytic domain where the actin binding and ATPfunctions of myosin take place. Once bound to an actin filament, therelease of phosphate (cf. ATP to ADP) leads to a change in structuralconformation of the catalytic domain that in turn alters the orientationof the light-chain binding lever arm domain that extends from theglobular head; this movement is termed the powerstroke. This change inorientation of the myosin head in relationship to actin causes the thickfilament of which it is a part to move with respect to the thin actinfilament to which it is bound. Un-binding of the globular head from theactin filament (also Ca²⁺ modulated) coupled with return of thecatalytic domain and light chain to their startingconformation/orientation completes the contraction and relaxation cycle,responsible for intracellular movement and muscle contraction.

Tropomyosin and troponin mediate the calcium effect on the interactionon actin and myosin. The skeletal troponin complex regulates the actionof several actin units at once, and is comprised of three polypepetidechains: skeletal troponin C, which binds calcium ions; troponin I, whichbinds to actin; and troponin T, which binds to tropomyosin.

Abnormal contraction of skeletal muscle is thought to be a pathogeneticcause of several disorders, including obesity, sarcopenia, wastingsyndrome, frailty, cachexia, muscle spasm, post-surgical andpost-traumatic muscle weakness, and neuromuscular disease, which poseserious health problems as adult diseases. The contraction andrelaxation of skeletal muscle are mainly controlled by increases anddecreases of intracellular calcium.

Myasthenia gravis is a chronic autoimmune neuromuscular disease whereinthe body produces antibodies that block, alter, or destroy proteinsinvolved in signaling at the neuromuscular junction, thus preventingmuscle contraction from occurring. These proteins include nicotinicacetylcholine receptor (AChR) or, less frequently, a muscle-specifictyrosine kinase (MuSK) involved in AChR clustering (see, e.g., Drachman,N. Eng. J. of Med., 330:1797-1810, 1994). The disease is characterizedby varying degrees of weakness of the skeletal (voluntary) muscles ofthe body. The hallmark of myasthenia gravis is muscle weakness thatincreases during periods of activity and improves after periods of rest.Although myasthenia gravis may affect any voluntary muscle, certainmuscles, such as those that control eye and eyelid movement, facialexpression, chewing, talking, and swallowing are often, but not always,involved in the disorder. The muscles that control breathing and neckand limb movements may also be affected.

In most cases, the first noticeable symptom is weakness of the eyemuscles. In others, difficulty in swallowing and slurred speech may bethe first signs. The degree of muscle weakness involved in myastheniagravis varies greatly among patients, ranging from a localized form,limited to eye muscles (ocular myasthenia), to a severe or generalizedform in which many muscles—sometimes including those that controlbreathing—are affected. Symptoms, which vary in type and severity, mayinclude a drooping of one or both eyelids (ptosis), blurred or doublevision (diplopia) due to weakness of the muscles that control eyemovements, unstable or waddling gait, weakness in arms, hands, fingers,legs, and neck, a change in facial expression, difficulty in swallowingand shortness of breath, and impaired speech (dysarthria). Generalizedweakness develops in approximately 85% of patients.

Current treatments for myasthenia gravis include anticholinesteraseagents (e.g., neostigmine, pyridostigmine), which help improveneuromuscular transmission and increase muscle strength, andimmunosuppressive drugs (e.g., prednisone, cyclosporine, azathioprine,mycophenolate mofetil) which improve muscle strength by suppressing theproduction of abnormal antibodies. Other therapies to treat myastheniagravis include thymectomy (i.e., the surgical removal of the thymusgland, which often is abnormal in myasthenia gravis patients),plasmapheresis, and intravenous immune globulin. Patients receivingthese medications or therapies must be monitored carefully because theymay cause serious side effects.

Accordingly, there is a need for the development of new compounds thattreat myasthenia gravis by exploiting new mechanisms of action and whichmay have better outcomes in terms of relief of symptoms, safety, andpatient mortality, both short-term and long-term and an improvedtherapeutic index. Such compounds may act, for example, by modulatingskeletal muscle performance or responsiveness to stimulation. Compoundsdisclosed herein act to sensitize fast skeletal muscle to motor neuronstimulation by interacting with the fast skeletal troponin complex(e.g., troponin C), resulting in sensitization of the skeletal myosinATPase to calcium. Such functional skeletal muscle troponin activatorsmay increase muscle force, increase muscle power and/or decrease musclefatigue in patients suffering from myasthenia gravis.

Provided is a method of treating myasthenia gravis in a patient byadministering to the patient an effective amount of a skeletal muscletroponin activator, or a pharmaceutically acceptable salt thereof. Insome embodiments, the at least one chemical entity is chosen fromcompounds of Formula I and compounds of Formula II:

and pharmaceutically acceptable salts thereof, wherein

R₁ and R₄ are independently selected from hydrogen, halo, hydroxy,optionally substituted acyl, optionally substituted alkyl, optionallysubstituted amino, optionally substituted alkenyl, optionallysubstituted alkynyl, optionally substituted cycloalkyl, optionallysubstituted heteroaryl, optionally substituted alkoxy, optionallysubstituted aminocarbonyl, sulfonyl, sulfanyl, sulfinyl, carboxy,optionally substituted alkoxycarbonyl, and cyano; and in thealternative, R₄ and R₁, taken together with any intervening atoms, forma fused ring system selected from optionally substituted fused aryl,optionally substituted fused heteroaryl, optionally substituted fusedcycloalkyl, and optionally substituted fused heterocycloalkyl; and

R₂ is selected from optionally substituted alkyl, optionally substitutedcycloalkyl, optionally substituted aryl, optionally substitutedheteroaryl, and optionally substituted heterocycloalkyl;

provided that

R₁ is not hex-1-enyl; and further provided that

the compound of Formula I or the compound of Formula II is not

-   (S)-6-bromo-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   1,5,6-trimethyl-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   1-methyl-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   6-bromo-1-(3-nitrobenzyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   5-(hydroxymethyl)-1,6-dimethyl-1H-imidazo[4,5-b]pyrazin-2(3H)-one;    or-   1-(piperidin-4-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one.

Also provided is a method of treating myasthenia gravis in a patient byadministering to the patient a pharmaceutically acceptable compositioncomprising a pharmaceutically acceptable carrier and at least oneskeletal muscle troponin activator.

Other aspects and embodiments will be apparent to those skilled in theart from the following detailed description.

DESCRIPTION OF FIGURES

FIGS. 1A and 1B are graphs depicting changes in body weight and forelimbgrip strength for female Sprague-Dawley rats injected intra-peritoneallywith either saline (control) or AChRα1/3/5 antibody.

FIG. 2 is a graph depicting changes in forelimb grip strength for femaleSprague-Dawley rats with induced experimental autoimmune myastheniagravis (EAMG) after treatment with vehicle (control) or neostigmine.

FIGS. 3A and 3B are graphs depicting changes in forelimb grip strengthfor control female Sprague-Dawley rats treated with vehicle or thecompound of Example 4.

FIGS. 4A and 4B are graphs depicting changes in forelimb grip strengthfor female Sprague-Dawley rats with induced experimental autoimmunemyasthenia gravis (EAMG) after treatment with vehicle (control) or thecompound of Example 4.

FIG. 5 is a graph depicting the change in the force of contractioncompared to baseline for the extensor digitorum longus muscle ofd-tubocurarine-treated male Sprague-Dawley rats after treatment withvehicle (control) or the compound of Example 4.

As used in the present specification, the following words and phrasesare generally intended to have the meanings as set forth below, exceptto the extent that the context in which they are used indicatesotherwise.

The following abbreviations and terms have the indicated meaningsthroughout:

-   Ac=acetyl-   APCI=atmospheric pressure chemical ionization-   atm=atomosphere-   Boc=tert-butoxycarbonyl-   c-=cyclo-   CBZ=carbobenzyloxy=benzyloxycarbonyl-   CDI=carbonyldiimidazole-   DCM=dichloromethane=methylene chloride=CH₂Cl₂-   DIEA=DIPEA=N,N-diisopropylethylamine-   DMF=N,N-dimethylformamide-   DMSO=dimethyl sulfoxide-   (DPPF)PdCl₂=[1,1′-bis(diphenylphosphino)ferrocene]dichloropalladium(II)-   Et=ethyl-   EtOAc=ethyl acetate-   EtOH=ethanol-   g=gram-   GC=gas chromatograghy-   h or hr=hour-   HPLC=high pressure liquid chromatography-   i-=iso-   kg or Kg=kilogram-   l or L=liter-   LCMS=liquid chromatography-mass spectrometry-   m/z=mass-to-charge ratio-   Me=methyl-   NMP=1-methyl-2-pyrrolidinone-   NMR=nuclear magnetic resonance-   MPLC=medium pressure liquid chromatography-   min=minute-   mg=milligram-   mL or ml=milliliter-   MW=microwave-   n-=normal-   Ph=phenyl-   (Ph₃P)₄Pd=tetrakis(triphenylphosphine)palladium(O)-   (Ph₃P)₂PdCl₂=dichlorobis(triphenylphosphine)palladium(II)-   rt or RT=room temperature-   s-=sec-=secondary-   t-=tert-=tertiary-   TES=triethylsilyl or triethylsilane-   TMS=trimethylsilyl or trimethylsilane-   TFA=trifluoroacetic acid-   THF=tetrahydrofuran-   TLC=thin layer chromatography-   UV=ultraviolet-   vol=volume equivalent in mL/g or L/Kg for the limiting reagent    unless otherwise indicated

By “optional” or “optionally” is meant that the subsequently describedevent or circumstance may or may not occur, and that the descriptionincludes instances where the event or circumstance occurs and instancesin which it does not. For example, “optionally substituted alkyl”encompasses both “alkyl” and “substituted alkyl” as defined below. Itwill be understood by those skilled in the art, with respect to anygroup containing one or more substituents, that such groups are notintended to introduce any substitution or substitution patterns that aresterically impractical, synthetically non-feasible, and/or inherentlyunstable.

“Alkyl” encompasses straight chain and branched chain having theindicated number of carbon atoms, usually from 1 to 20 carbon atoms, forexample 1 to 8 carbon atoms, such as 1 to 6 carbon atoms. For exampleC₁-C₆ alkyl encompasses both straight and branched chain alkyl of from 1to 6 carbon atoms. When an alkyl residue having a specific number ofcarbons is named, all branched and straight chain versions having thatnumber of carbons are intended to be encompassed; thus, for example,“butyl” is meant to include n-butyl, sec-butyl, isobutyl and t-butyl;“propyl” includes n-propyl and isopropyl. “Lower alkyl” refers to alkylgroups having one to seven carbons. In certain embodiments, “loweralkyl” refers to alkyl groups having one to six carbons. Examples ofalkyl groups include methyl, ethyl, propyl, isopropyl, n-butyl,sec-butyl, tert-butyl, pentyl, 2-pentyl, isopentyl, neopentyl, hexyl,2-hexyl, 3-hexyl, 3-methylpentyl, and the like. Alkylene is a subset ofalkyl, referring to the same residues as alkyl, but having two points ofattachment. Alkylene groups will usually have from 2 to 20 carbon atoms,for example 2 to 8 carbon atoms, such as from 2 to 6 carbon atoms. Forexample, C₀ alkylene indicates a covalent bond and C₁ alkylene is amethylene group.

“Alkenyl” refers to an unsaturated branched or straight-chain alkylgroup having at least one carbon-carbon double bond derived by theremoval of one molecule of hydrogen from adjacent carbon atoms of theparent alkyl. The group may be in either the cis or trans configurationabout the double bond(s). Typical alkenyl groups include, but are notlimited to, ethenyl; propenyls such as prop-1-en-1-yl, prop-1-en-2-yl,prop-2-en-1-yl(allyl), prop-2-en-2-yl; butenyls such as but-1-en-1-yl,but-1-en-2-yl, 2-methyl-prop-1-en-1-yl, but-2-en-1-yl, but-2-en-1-yl,but-2-en-2-yl, buta-1,3-dien-1-yl, buta-1,3-dien-2-yl; and the like. Incertain embodiments, an alkenyl group has from 2 to 20 carbon atoms andin other embodiments, from 2 to 6 carbon atoms. “Lower alkenyl” refersto alkenyl groups having two to six carbons.

“Alkynyl” refers to an unsaturated branched or straight-chain alkylgroup having at least one carbon-carbon triple bond derived by theremoval of two molecules of hydrogen from adjacent carbon atoms of theparent alkyl. Typical alkynyl groups include, but are not limited to,ethynyl; propynyls such as prop-1-yn-1-yl, prop-2-yn-1-yl; butynyls suchas but-1-yn-1-yl, but-1-yn-3-yl, but-3-yn-1-yl; and the like. In certainembodiments, an alkynyl group has from 2 to 20 carbon atoms and in otherembodiments, from 3 to 6 carbon atoms. “Lower alkynyl” refers to alkynylgroups having two to six carbons.

“Cycloalkyl” indicates a non-aromatic carbocyclic ring, usually havingfrom 3 to 7 ring carbon atoms. The ring may be saturated or have one ormore carbon-carbon double bonds. Examples of cycloalkyl groups includecyclopropyl, cyclobutyl, cyclopentyl, cyclopentenyl, cyclohexyl, andcyclohexenyl, as well as bridged and caged ring groups such asnorbornane.

The term “alkoxy” refers to the group —O-alkyl, including from 1 to 8carbon atoms of a straight, branched, cyclic configuration andcombinations thereof attached to the parent structure through an oxygen.Examples include methoxy, ethoxy, propoxy, isopropoxy, cyclopropyloxy,cyclohexyloxy and the like. “Lower alkoxy” refers to alkoxy groupscontaining one to six carbons.

The term “substituted alkoxy” refers to alkoxy wherein the alkylconstituent is substituted (i.e., —O-(substituted alkyl)) wherein“substituted alkyl” refers to alkyl wherein one or more (such as up to5, for example, up to 3) hydrogen atoms are replaced by a substituentindependently chosen from:

—R^(a), —OR^(b), optionally substituted amino (including —NR^(c)COR^(b),—NR^(c)CO₂R^(a), —NR^(c)CONR^(b)R^(c), —NR^(b)C(NR^(c))NR^(b)R^(c),—NR^(b)C(NCN)NR^(b)R^(c), and —NR^(c)SO₂R^(a)), halo, cyano, nitro, oxo(as a substitutent for cycloalkyl, heterocycloalkyl, and heteroaryl),optionally substituted acyl (such as —COR^(b)), optionally substitutedalkoxycarbonyl (such as —CO₂R^(b)), aminocarbonyl (such as—CONR^(b)R^(c)), —OCOR^(b), —OCO₂R^(a), —OCONR^(b)R^(c),—OCONR^(b)R^(c), —OP(O)(OR^(b))OR^(c), sulfanyl (such as SR^(b)),sulfinyl (such as —SOR^(a)), and sulfonyl (such as —SO₂R^(a) and—SO₂NR^(b)R^(c)),

where R^(a) is chosen from optionally substituted C₁-C₆ alkyl,optionally substituted alkenyl, optionally substituted alkynyl,optionally substituted aryl, and optionally substituted heteroaryl;

R^(b) is chosen from H, optionally substituted C₁-C₆ alkyl, optionallysubstituted cycloalkyl, optionally substituted heterocycloalkyl,optionally substituted aryl, and optionally substituted heteroaryl; and

R^(c) is independently chosen from hydrogen and optionally substitutedC₁-C₄ alkyl; or

R^(b) and R^(c), and the nitrogen to which they are attached, form anoptionally substituted heterocycloalkyl group; and

where each optionally substituted group is unsubstituted orindependently substituted with one or more, such as one, two, or three,substituents independently selected from C₁-C₄ alkyl, aryl, heteroaryl,aryl-C₁-C₄ alkyl-, heteroaryl-C₁-C₄ alkyl-, C₁-C₄ haloalkyl, —OC₁-C₄alkyl, —OC₁-C₄ alkylphenyl, —C₁-C₄ alkyl-OH, —OC₁-C₄ haloalkyl, halo,—OH, —NH₂, —C₁-C₄ alkyl-NH₂, —N(C₁-C₄ alkyl)(C₁-C₄ alkyl), —NH(C₁-C₄alkyl), —N(C₁-C₄ alkyl)(C₁-C₄ alkylphenyl), —NH(C₁-C₄ alkylphenyl),cyano, nitro, oxo (as a substitutent for cycloalkyl, heterocycloalkyl,or heteroaryl), —CO₂H, —C(O)OC₁-C₄ alkyl, —CON(C₁-C₄ alkyl)(C₁-C₄alkyl), —CONH(C₁-C₄ alkyl), —CONH₂, —NHC(O)(C₁-C₄ alkyl),—NHC(O)(phenyl), —N(C₁-C₄ alkyl)C(O)(C₁-C₄ alkyl), —N(C₁-C₄alkyl)C(O)(phenyl), —C(O)C₁-C₄ alkyl, —C(O)C₁-C₄ alkylphenyl, —C(O)C₁-C₄haloalkyl, —OC(O)C₁-C₄ alkyl, —SO₂(C₁-C₄ alkyl), —SO₂(phenyl),—SO₂(C₁-C₄ haloalkyl), —SO₂NH₂, —SO₂NH(C₁-C₄ alkyl), —SO₂NH(phenyl),—NHSO₂(C₁-C₄ alkyl), —NHSO₂(phenyl), and —NHSO₂(C₁-C₄ haloalkyl).

In some embodiments, a substituted alkoxy group is “polyalkoxy” or —O—(optionally substituted alkylene)-(optionally substituted alkoxy), andincludes groups such as —OCH₂CH₂OCH₃, and residues of glycol ethers suchas polyethyleneglycol, and —O(CH₂CH₂O)_(x)CH₃, where x is an integer of2-20, such as 2-10, and for example, 2-5. Another substituted alkoxygroup is hydroxyalkoxy or —OCH₂(CH₂)_(y)OH, where y is an integer of1-10, such as 1-4.

The term “alkoxycarbonyl” refers to a group of the formula(alkoxy)(C═O)— attached through the carbonyl carbon wherein the alkoxygroup has the indicated number of carbon atoms. Thus a C₁-C₆alkoxycarbonyl group is an alkoxy group having from 1 to 6 carbon atomsattached through its oxygen to a carbonyl linker. “Lower alkoxycarbonyl”refers to an alkoxycarbonyl group wherein the alkoxy group is a loweralkoxy group.

The term “substituted alkoxycarbonyl” refers to the group (substitutedalkyl)-O—C(O)— wherein the group is attached to the parent structurethrough the carbonyl functionality and wherein substituted refers toalkyl wherein one or more (such as up to 5, for example, up to 3)hydrogen atoms are replaced by a substituent independently chosen from:

—R^(a), —OR^(b), optionally substituted amino (including —NR^(c)COR^(b),—NR^(c)CO₂R^(a), —NR^(c)CONR^(b)R^(c), —NR^(b)C(NR^(c))NR^(b)R^(c),—NR^(b)C(NCN)NR^(b)R^(c), and —NR^(c)SO₂R^(a)), halo, cyano, nitro, oxo(as a substitutent for cycloalkyl, heterocycloalkyl, and heteroaryl),optionally substituted acyl (such as —COR^(b)), optionally substitutedalkoxycarbonyl (such as —CO₂R^(b)), aminocarbonyl (such as—CONR^(b)R^(c)), —OCOR^(b), —OCO₂R^(a), —OCONR^(b)R^(c),—OCONR^(b)R^(c), —OP(O)(OR^(b))OR^(c), sulfanyl (such as SR^(b)),sulfinyl (such as —SOR^(a)), and sulfonyl (such as —SO₂R^(a) and—SO₂NR^(b)R^(c)),

where R^(a) is chosen from optionally substituted C₁-C₆ alkyl,optionally substituted alkenyl, optionally substituted alkynyl,optionally substituted aryl, and optionally substituted heteroaryl;

R^(b) is chosen from H, optionally substituted C₁-C₆ alkyl, optionallysubstituted cycloalkyl, optionally substituted heterocycloalkyl,optionally substituted aryl, and optionally substituted heteroaryl; and

R^(c) is independently chosen from hydrogen and optionally substitutedC₁-C₄ alkyl; or

R^(b) and R^(c), and the nitrogen to which they are attached, form anoptionally substituted heterocycloalkyl group; and

where each optionally substituted group is unsubstituted orindependently substituted with one or more, such as one, two, or three,substituents independently selected from C₁-C₄ alkyl, aryl, heteroaryl,aryl-C₁-C₄ alkyl-, heteroaryl-C₁-C₄ alkyl-, C₁-C₄ haloalkyl, —OC₁-C₄alkyl, —OC₁-C₄ alkylphenyl, —C₁-C₄ alkyl-OH, —OC₁-C₄ haloalkyl, halo,—OH, —NH₂, —C₁-C₄ alkyl-NH₂, —N(C₁-C₄ alkyl)(C₁-C₄ alkyl), —NH(C₁-C₄alkyl), —N(C₁-C₄ alkyl)(C₁-C₄ alkylphenyl), —NH(C₁-C₄ alkylphenyl),cyano, nitro, oxo (as a substitutent for cycloalkyl, heterocycloalkyl,or heteroaryl), —CO₂H, —C(O)OC₁-C₄ alkyl, —CON(C₁-C₄ alkyl)(C₁-C₄alkyl), —CONH(C₁-C₄ alkyl), —CONH₂, —NHC(O)(C₁-C₄ alkyl),—NHC(O)(phenyl), —N(C₁-C₄ alkyl)C(O)(C₁-C₄ alkyl), —N(C₁-C₄alkyl)C(O)(phenyl), —C(O)C₁-C₄ alkyl, —C(O)C₁-C₄ alkylphenyl, —C(O)C₁-C₄haloalkyl, —OC(O)C₁-C₄ alkyl, —SO₂(C₁-C₄ alkyl), —SO₂(phenyl),—SO₂(C₁-C₄ haloalkyl), —SO₂NH₂, —SO₂NH(C₁-C₄ alkyl), —SO₂NH(phenyl),—NHSO₂(C₁-C₄ alkyl), —NHSO₂(phenyl), and —NNSO₂(C₁-C₄ haloalkyl).

“Acyl” refers to the groups H—C(O)—, (alkyl)-C(O)—, (aryl)-C(O)—,(heteroaryl)-C(O)—, and (heterocycloalkyl)-C(O)—, wherein the group isattached to the parent structure through the carbonyl functionality, andwherein alkyl, aryl, heteroaryl, and heterocycloalkyl are optionallysubstituted as described herein. Examples include acetyl, benzoyl,propionyl, isobutyryl, t-butoxycarbonyl, benzyloxycarbonyl and the like.“Lower-acyl” refers to groups containing one to six carbons and“acyloxy” refers to the group O-acyl.

The term “amino” refers to the group —NH₂.

The term “substituted amino” refers to the group —NHR^(d) or—NR^(d)R^(e) wherein

R^(d) is chosen from hydroxy, optionally substituted alkoxy, optionallysubstituted alkyl, optionally substituted cycloalkyl, optionallysubstituted acyl, optionally substituted carbamimidoyl, aminocarbonyl,optionally substituted aryl, optionally substituted heteroaryl,optionally substituted heterocycloalkyl, optionally substitutedalkoxycarbonyl, sulfinyl and sulfonyl, and

R^(e) is chosen from optionally substituted alkyl, optionallysubstituted cycloalkyl, optionally substituted aryl, optionallysubstituted heteroaryl, and optionally substituted heterocycloalkyl, andwherein

substituted alkyl, cycloalkyl, aryl, heterocycloalkyl, and heteroarylrefer respectively to alkyl, cycloalkyl, aryl, heterocycloalkyl, andheteroaryl wherein one or more (such as up to 5, for example, up to 3)hydrogen atoms are replaced by a substituent independently chosen from:

—R^(a), —OR^(b), optionally substituted amino (including —NR^(c)COR^(b),—NR^(c)CO₂R^(a), —NR^(c)CONR^(b)R^(c), —NR^(b)C(NR^(c))NR^(b)R^(c),—NR^(b)C(NCN)NR^(b)R^(c), and —NR^(c)SO₂R^(a)), halo, cyano, nitro, oxo(as a substitutent for cycloalkyl, heterocycloalkyl, and heteroaryl),optionally substituted acyl (such as —COR^(b)), optionally substitutedalkoxycarbonyl (such as —CO₂R^(b)), aminocarbonyl (such as—CONR^(b)R^(c)), —OCOR^(b), —OCO₂R^(a), —OCONR^(b)R^(c),—OCONR^(b)R^(c), —OP(O)(OR^(b))OR^(c), sulfanyl (such as SR^(b)),sulfinyl (such as —SOR^(a)), and sulfonyl (such as —SO₂R^(a) and—SO₂NR^(b)R^(c)), where

R^(a) is chosen from optionally substituted C₁-C₆ alkyl, optionallysubstituted alkenyl, optionally substituted alkynyl, optionallysubstituted aryl, and optionally substituted heteroaryl;

R^(b) is chosen from H, optionally substituted C₁-C₆ alkyl, optionallysubstituted cycloalkyl, optionally substituted heterocycloalkyl,optionally substituted aryl, and optionally substituted heteroaryl; and

R^(c) is independently chosen from hydrogen and optionally substitutedC₁-C₄ alkyl; or R^(b) and R^(c), and the nitrogen to which they areattached, form an optionally substituted heterocycloalkyl group; andwhere each optionally substituted group is unsubstituted orindependently substituted with one or more, such as one, two, or three,substituents independently selected from C₁-C₄ alkyl, aryl, heteroaryl,aryl-C₁-C₄ alkyl-, heteroaryl-C₁-C₄ alkyl-, C₁-C₄ haloalkyl, —OC₁-C₄alkyl, —OC₁-C₄ alkylphenyl, —C₁-C₄ alkyl-OH, —OC₁-C₄ haloalkyl, halo,—OH, —NH₂, —C₁-C₄ alkyl-NH₂, —N(C₁-C₄ alkyl)(C₁-C₄ alkyl), —NH(C₁-C₄alkyl), —N(C₁-C₄ alkyl)(C₁-C₄ alkylphenyl), —NH(C₁-C₄ alkylphenyl),cyano, nitro, oxo (as a substitutent for cycloalkyl, heterocycloalkyl,or heteroaryl), —CO₂H, —C(O)OC₁-C₄ alkyl, —CON(C₁-C₄ alkyl)(C₁-C₄alkyl), —CONH(C₁-C₄ alkyl), —CONH₂, —NHC(O)(C₁-C₄ alkyl),—NHC(O)(phenyl), —N(C₁-C₄ alkyl)C(O)(C₁-C₄ alkyl), —N(C₁-C₄alkyl)C(O)(phenyl), —C(O)C₁-C₄ alkyl, —C(O)C₁-C₄ alkylphenyl, —C(O)C₁-C₄haloalkyl, —OC(O)C₁-C₄ alkyl, —SO₂(C₁-C₄ alkyl), —SO₂(phenyl),—SO₂(C₁-C₄ haloalkyl), —SO₂NH₂, —SO₂NH(C₁-C₄ alkyl), —SO₂NH(phenyl),—NHSO₂(C₁-C₄ alkyl), —NHSO₂(phenyl), and —NHSO₂(C₁-C₄ haloalkyl); andwherein

optionally substituted acyl, optionally substituted alkoxycarbonyl,sulfinyl and sulfonyl are as defined herein.

The term “substituted amino” also refers to N-oxides of the groups—NHR^(d), and NR^(d)R^(d) each as described above. N-oxides can beprepared by treatment of the corresponding amino group with, forexample, hydrogen peroxide or m-chloroperoxybenzoic acid. The personskilled in the art is familiar with reaction conditions for carrying outthe N-oxidation.

The term “aminocarbonyl” refers to the group —CONR^(b)R^(c), where R^(b)is chosen from H, optionally substituted C₁-C₆ alkyl, optionallysubstituted cycloalkyl, optionally substituted heterocycloalkyl,optionally substituted aryl, and optionally substituted heteroaryl; and

R^(c) is independently chosen from hydrogen and optionally substitutedC₁-C₄ alkyl; or

R^(b) and R^(c) taken together with the nitrogen to which they arebound, form an optionally substituted 5- to 7-memberednitrogen-containing heterocycloalkyl which optionally includes 1 or 2additional heteroatoms selected from O, N, and S in the heterocycloalkylring;

where each substituted group is independently substituted with one ormore substituents independently selected from C₁-C₄ alkyl, aryl,heteroaryl, aryl-C₁-C₄ alkyl-, heteroaryl-C₁-C₄ alkyl-, C₁-C₄ haloalkyl,—OC₁-C₄ alkyl, —OC₁-C₄ alkylphenyl, —C₁-C₄ alkyl-OH, —OC₁-C₄ haloalkyl,halo, —OH, —NH₂, —C₁-C₄ alkyl-NH₂, —N(C₁-C₄ alkyl)(C₁-C₄ alkyl),—NH(C₁-C₄ alkyl), —N(C₁-C₄ alkyl)(C₁-C₄ alkylphenyl), —NH(C₁-C₄alkylphenyl), cyano, nitro, oxo (as a substitutent for cycloalkyl,heterocycloalkyl, or heteroaryl), —CO₂H, —C(O)OC₁-C₄ alkyl, —CON(C₁-C₄alkyl)(C₁-C₄ alkyl), —CONH(C₁-C₄ alkyl), —CONH₂, —NHC(O)(C₁-C₄ alkyl),—NHC(O)(phenyl), —N(C₁-C₄ alkyl)C(O)(C₁-C₄ alkyl), —N(C₁-C₄alkyl)C(O)(phenyl), —C(O)C₁-C₄ alkyl, —C(O)C₁-C₄ alkylphenyl, —C(O)C₁-C₄haloalkyl, —OC(O)C₁-C₄ alkyl, —SO₂(C₁-C₄ alkyl), —SO₂(phenyl),—SO₂(C₁-C₄ haloalkyl), —SO₂NH₂, —SO₂NH(C₁-C₄ alkyl), —SO₂NH(phenyl),—NHSO₂(C₁-C₄ alkyl), —NHSO₂(phenyl), and —NHSO₂(C₁-C₄ haloalkyl).

“Aryl” encompasses:

6-membered carbocyclic aromatic rings, for example, benzene;

bicyclic ring systems wherein at least one ring is carbocyclic andaromatic, for example, naphthalene, indane, and tetralin; and

tricyclic ring systems wherein at least one ring is carbocyclic andaromatic, for example, fluorene.

For example, aryl includes 6-membered carbocyclic aromatic rings fusedto a 5- to 7-membered heterocycloalkyl ring containing 1 or moreheteroatoms chosen from N, O, and S. For such fused, bicyclic ringsystems wherein only one of the rings is a carbocyclic aromatic ring,the point of attachment may be at the carbocyclic aromatic ring or theheterocycloalkyl ring. Bivalent radicals formed from substituted benzenederivatives and having the free valences at ring atoms are named assubstituted phenylene radicals. Bivalent radicals derived from univalentpolycyclic hydrocarbon radicals whose names end in “-yl” by removal ofone hydrogen atom from the carbon atom with the free valence are namedby adding “-idene” to the name of the corresponding univalent radical,e.g., a naphthyl group with two points of attachment is termednaphthylidene. Aryl, however, does not encompass or overlap in any waywith heteroaryl, separately defined below. Hence, if one or morecarbocyclic aromatic rings is fused with a heterocycloalkyl aromaticring, the resulting ring system is heteroaryl, not aryl, as definedherein.

“Aralkoxy” refers to the group —O-aralkyl. Similarly, “heteroaralkoxy”refers to the group —O-heteroaralkyl; “aryloxy” refers to —O-aryl; and“heteroaryloxy” refers to the group —O-heteroaryl.

“Aralkyl” refers to a residue in which an aryl moiety is attached to theparent structure via an alkyl residue. Examples include benzyl,phenethyl, phenylvinyl, phenylallyl and the like. “Heteroaralkyl” refersto a residue in which a heteroaryl moiety is attached to the parentstructure via an alkyl residue. Examples include furanylmethyl,pyridinylmethyl, pyrimidinylethyl and the like.

“Halogen” or “halo” refers to fluorine, chlorine, bromine or iodine.Dihaloaryl, dihaloalkyl, trihaloaryl etc. refer to aryl and alkylsubstituted with a plurality of halogens, but not necessarily aplurality of the same halogen; thus 4-chloro-3-fluorophenyl is withinthe scope of dihaloaryl.

“Heteroaryl” encompasses:

5- to 7-membered aromatic, monocyclic rings containing one or more, forexample, from 1 to 4, or in certain embodiments, from 1 to 3,heteroatoms chosen from N, O, and S, with the remaining ring atoms beingcarbon;

bicyclic heterocycloalkyl rings containing one or more, for example,from 1 to 4, or in certain embodiments, from 1 to 3, heteroatoms chosenfrom N, O, and S, with the remaining ring atoms being carbon and whereinat least one heteroatom is present in an aromatic ring; and

tricyclic heterocycloalkyl rings containing one or more, for example,from 1 to 5, or in certain embodiments, from 1 to 4, heteroatoms chosenfrom N, O, and S, with the remaining ring atoms being carbon and whereinat least one heteroatom is present in an aromatic ring.

For example, heteroaryl includes a 5- to 7-membered heterocycloalkyl,aromatic ring fused to a 5- to 7-membered cycloalkyl or heterocycloalkylring. For such fused, bicyclic heteroaryl ring systems wherein only oneof the rings contains one or more heteroatoms, the point of attachmentmay be at either ring. When the total number of S and O, atoms in theheteroaryl group exceeds 1, those heteroatoms are not adjacent to oneanother. In certain embodiments, the total number of S and O atoms inthe heteroaryl group is not more than 2. In certain embodiments, thetotal number of S and O atoms in the aromatic heterocycle is not morethan 1. Examples of heteroaryl groups include, but are not limited to,(as numbered from the linkage position assigned priority 1), 2-pyridyl,3-pyridyl, 4-pyridyl, 2,3-pyrazinyl, 3,4-pyrazinyl, 2,4-pyrimidinyl,3,5-pyrimidinyl, 2,3-pyrazolinyl, 2,4-imidazolinyl, isoxazolinyl,oxazolinyl, thiazolinyl, thiadiazolinyl, tetrazolyl, thienyl,benzothiophenyl, furanyl, benzofuranyl, benzoimidazolinyl, indolinyl,pyridazinyl, triazolyl, quinolinyl, pyrazolyl, and5,6,7,8-tetrahydroisoquinolinyl. Bivalent radicals derived fromunivalent heteroaryl radicals whose names end in “-yl” by removal of onehydrogen atom from the atom with the free valence are named by adding“-idene” to the name of the corresponding univalent radical, e.g., apyridyl group with two points of attachment is a pyridylidene.Heteroaryl does not encompass or overlap with aryl, cycloalkyl, orheterocycloalkyl, as defined herein

Substituted heteroaryl also includes ring systems substituted with oneor more oxide (—O⁻) substituents, such as pyridinyl N-oxides.

By “heterocycloalkyl” is meant a single, non-aromatic ring, usually with3 to 7 ring atoms, containing at least 2 carbon atoms in addition to 1-3heteroatoms independently selected from oxygen, sulfur, and nitrogen, aswell as combinations comprising at least one of the foregoingheteroatoms. The ring may be saturated or have one or more carbon-carbondouble bonds. Suitable heterocycloalkyl groups include, for example (asnumbered from the linkage position assigned priority 1), 2-pyrrolidinyl,2,4-imidazolidinyl, 2,3-pyrazolidinyl, 2-piperidyl, 3-piperidyl,4-piperidyl, and 2,5-piperizinyl. Morpholinyl groups are alsocontemplated, including 2-morpholinyl and 3-morpholinyl (numberedwherein the oxygen is assigned priority 1). Substituted heterocycloalkylalso includes ring systems substituted with one or more oxo (═O) oroxide (—O⁻) substituents, such as piperidinyl N-oxide,morpholinyl-N-oxide, 1-oxo-1-thiomorpholinyl and1,1-dioxo-1-thiomorpholinyl.

“Heterocycloalkyl” also includes bicyclic ring systems wherein onenon-aromatic ring, usually with 3 to 7 ring atoms, contains at least 2carbon atoms in addition to 1-3 heteroatoms independently selected fromoxygen, sulfur, and nitrogen, as well as combinations comprising atleast one of the foregoing heteroatoms; and the other ring, usually with3 to 7 ring atoms, optionally contains 1-3 heteratoms independentlyselected from oxygen, sulfur, and nitrogen and is not aromatic.

“Isomers” are different compounds that have the same molecular formula.“Stereoisomers” are isomers that differ only in the way the atoms arearranged in space. “Enantiomers” are a pair of stereoisomers that arenon-superimposable mirror images of each other. A 1:1 mixture of a pairof enantiomers is a “racemic” mixture. The term “(.±.)” is used todesignate a racemic mixture where appropriate.

“Diastereoisomers” are stereoisomers that have at least two asymmetricatoms, but which are not mirror-images of each other. The absolutestereochemistry is specified according to the Cahn-Ingold-Prelog R—Ssystem. When a compound is a pure enantiomer the stereochemistry at eachchiral carbon can be specified by either R or S. Resolved compoundswhose absolute configuration is unknown can be designated (+) or (−)depending on the direction (dextro- or levorotatory) which they rotateplane polarized light at the wavelength of the sodium D line. Certain ofthe compounds described herein contain one or more asymmetric centersand can thus give rise to enantiomers, diastereomers, and otherstereoisomeric forms that can be defined, in terms of absolutestereochemistry, as (R)— or (S)—. The present invention is meant toinclude all such possible isomers, including racemic mixtures, opticallypure forms and intermediate mixtures. Optically active (R)- and(S)-isomers can be prepared using chiral synthons or chiral reagents, orresolved using conventional techniques. When the compounds describedherein contain olefinic double bonds or other centers of geometricasymmetry, and unless specified otherwise, it is intended that thecompounds include both E and Z geometric isomers.

“Tautomers” are structurally distinct isomers that interconvert bytautomerization. “Tautomerization” is a form of isomerization andincludes prototropic or proton-shift tautomerization, which isconsidered a subset of acid-base chemistry. “Prototropictautomerization” or “proton-shift tautomerization” involves themigration of a proton accompanied by changes in bond order, often theinterchange of a single bond with an adjacent double bond. Wheretautomerization is possible (e.g. in solution), a chemical equilibriumof tautomers can be reached. An example of tautomerization is keto-enoltautomerization. A specific example of keto-enol tautomerization is theinterconverision of pentane-2,4-dione and 4-hydroxypent-3-en-2-onetautomers. Another example of tautomerization is phenol-ketotautomerization. A specific example of phenol-keto tautomerization isthe interconverision of pyridin-4-ol and pyridin-4(1H)-one tautomers.Compounds of Formula I and compounds of Formula II are tautomeric.

A leaving group or atom is any group or atom that will, under thereaction conditions, cleave from the starting material, thus promotingreaction at a specified site. Suitable examples of such groups unlessotherwise specified are halogen atoms, mesyloxy,p-nitrobenzensulphonyloxy and tosyloxy groups.

The term “pharmaceutically acceptable carrier” or “pharmaceuticallyacceptable excipient” includes any and all solvents, dispersion media,coatings, antibacterial and antifungal agents, isotonic and absorptiondelaying agents and the like. The use of such media and agents forpharmaceutically active substances is well known in the art. Exceptinsofar as any conventional media or agent is incompatible with theactive ingredient, its use in the therapeutic compositions iscontemplated. Supplementary active ingredients can also be incorporatedinto the compositions.

Protecting group has the meaning conventionally associated with it inorganic synthesis, i.e. a group that selectively blocks one or morereactive sites in a multifunctional compound such that a chemicalreaction can be carried out selectively on another unprotected reactivesite and such that the group can readily be removed after the selectivereaction is complete. A variety of protecting groups are disclosed, forexample, in T. H. Greene and P. G. M. Wuts, Protective Groups in OrganicSynthesis, Third Edition, John Wiley & Sons, New York (1999). Forexample, a hydroxy protected form is where at least one of the hydroxygroups present in a compound is protected with a hydroxy protectinggroup. Likewise, amines and other reactive groups may similarly beprotected.

The term “pharmaceutically acceptable salt” refers to salts that retainthe biological effectiveness and properties of the compounds describedherein and, which are not biologically or otherwise undesirable. In manycases, the compounds described herein are capable of forming acid and/orbase salts by virtue of the presence of amino and/or carboxyl groups orgroups similar thereto. Pharmaceutically acceptable acid addition saltscan be formed with inorganic acids and organic acids. Inorganic acidsfrom which salts can be derived include, for example, hydrochloric acid,hydrobromic acid, sulfuric acid, nitric acid, phosphoric acid, and thelike. Organic acids from which salts can be derived include, forexample, acetic acid, propionic acid, glycolic acid, pyruvic acid,oxalic acid, maleic acid, malonic acid, succinic acid, fumaric acid,tartaric acid, citric acid, benzoic acid, cinnamic acid, mandelic acid,methanesulfonic acid, ethanesulfonic acid, p-toluenesulfonic acid,salicylic acid, and the like. Pharmaceutically acceptable base additionsalts can be formed with inorganic and organic bases. Inorganic basesfrom which salts can be derived include, for example, sodium, potassium,lithium, ammonium, calcium, magnesium, iron, zinc, copper, manganese,aluminum, and the like. Organic bases from which salts can be derivedinclude, for example, primary, secondary, and tertiary amines,substituted amines including naturally occurring substituted amines,cyclic amines, basic ion exchange resins, and the like, specificallysuch as isopropylamine, trimethylamine, diethylamine, triethylamine,tripropylamine, and ethanolamine. In some embodiments, thepharmaceutically acceptable base addition salt is chosen from ammonium,potassium, sodium, calcium, and magnesium salts.

The term “solvate” refers to a compound (e.g., a compound selected fromFormula I and Formula II, or a pharmaceutically acceptable salt thereof)in physical association with one or more molecules of a pharmaceuticallyacceptable solvent. It will be understood that “a compound of Formula I”and “a compound of Formula II” encompass the compound of Formula I andthe compound of Formula II, and solvates of those compounds, as well asmixtures thereof.

The terms “substituted” alkyl, cycloalkyl, aryl, heterocycloalkyl, andheteroaryl, unless otherwise expressly defined, refer respectively toalkyl, cycloalkyl, aryl, heterocycloalkyl, and heteroaryl wherein one ormore (such as up to 5, for example, up to 3) hydrogen atoms are replacedby a substituent independently chosen from:

—R^(a), —OR^(b), optionally substituted amino (including —NR^(c)COR^(b),—NR^(c)CO₂R^(a), —NR^(c)CONR^(b)R^(c), —NR^(b)C(NR^(c))NR^(b)R^(c),—NR^(b)C(NCN)NR^(b)R^(c), and —NR^(c)SO₂R^(a)), halo, cyano, nitro, oxo(as a substitutent for cycloalkyl, heterocycloalkyl, and heteroaryl),optionally substituted acyl (such as —COR^(b)), optionally substitutedalkoxycarbonyl (such as —CO₂R^(b)), aminocarbonyl (such as—CONR^(b)R^(c)), —OCOR^(b), —OCO₂R^(a), —OCONR^(b)R^(c),—OCONR^(b)R^(c), —OP(O)(OR^(b))OR^(c), sulfanyl (such as SR^(b)),sulfinyl (such as —SOR^(a)), and sulfonyl (such as —SO₂R^(a) and—SO₂NR^(b)R^(c)), where

R^(a) is chosen from optionally substituted C₁-C₆ alkyl, optionallysubstituted cycloalkyl, optionally substituted heterocycloalkyl,optionally substituted alkenyl, optionally substituted alkynyl,optionally substituted aryl, and optionally substituted heteroaryl;

R^(b) is chosen from hydrogen, optionally substituted C₁-C₆ alkyl,optionally substituted cycloalkyl, optionally substitutedheterocycloalkyl, optionally substituted aryl, and optionallysubstituted heteroaryl; and

R^(c) is independently chosen from hydrogen and optionally substitutedC₁-C₄ alkyl; or

R^(b) and R^(c), and the nitrogen to which they are attached, form anoptionally substituted heterocycloalkyl group; and

where each optionally substituted group is unsubstituted orindependently substituted with one or more, such as one, two, or three,substituents independently selected from C₁-C₄ alkyl, aryl, heteroaryl,aryl-C₁-C₄ alkyl-, heteroaryl-C₁-C₄ alkyl-, C₁-C₄ haloalkyl, —OC₁-C₄alkyl, —OC₁-C₄ alkylphenyl, —C₁-C₄ alkyl-OH, —OC₁-C₄ haloalkyl, halo,—OH, —NH₂, —C₁-C₄ alkyl-NH₂, —N(C₁-C₄ alkyl)(C₁-C₄ alkyl), —NH(C₁-C₄alkyl), —N(C₁-C₄ alkyl)(C₁-C₄ alkylphenyl), —NH(C₁-C₄ alkylphenyl),cyano, nitro, oxo (as a substitutent for cycloalkyl orheterocycloalkyl), —CO₂H, —C(O)OC₁-C₄ alkyl, —CON(C₁-C₄ alkyl)(C₁-C₄alkyl), —CONH(C₁-C₄ alkyl), —CONH₂, —NHC(O)(C₁-C₄ alkyl),—NHC(O)(phenyl), —N(C₁-C₄ alkyl)C(O)(C₁-C₄ alkyl), —N(C₁-C₄alkyl)C(O)(phenyl), —C(O)C₁-C₄ alkyl, —C(O)C₁-C₄ alkylphenyl, —C(O)C₁-C₄haloalkyl, —OC(O)C₁-C₄ alkyl, —SO₂(C₁-C₄ alkyl), —SO₂(phenyl),—SO₂(C₁-C₄ haloalkyl), —SO₂NH₂, —SO₂NH(C₁-C₄ alkyl), —SO₂NH(phenyl),—NHSO₂(C₁-C₄ alkyl), —NHSO₂(phenyl), and —NHSO₂(C₁-C₄ haloalkyl).

The term “sulfanyl” refers to the groups: —S-(optionally substitutedalkyl), —S-(optionally substituted cycloalkyl), —S-(optionallysubstituted aryl), —S-(optionally substituted heteroaryl), and—S-(optionally substituted heterocycloalkyl).

The term “sulfinyl” refers to the groups: —S(O)—H, —S(O)-(optionallysubstituted alkyl), —S(O)-(optionally substituted cycloalkyl),—S(O)-(optionally substituted amino), —S(O)-(optionally substitutedaryl), —S(O)-(optionally substituted heteroaryl), and —S(O)-(optionallysubstituted heterocycloalkyl).

The term “sulfonyl” refers to the groups: —S(O₂)—H, —S(O₂)-(optionallysubstituted alkyl), —S(O₂)-(optionally substituted cycloalkyl),—S(O₂)-(optionally substituted amino), —S(O₂)-(optionally substitutedaryl), —S(O₂)-(optionally substituted heteroaryl), and—S(O₂)-(optionally substituted heterocycloalkyl).

The term “therapeutically effective amount” or “effective amount” refersto that amount of a compound selected from Formula I and Formula II thatis sufficient to effect treatment, as defined below, when administeredto a mammal in need of such treatment. The therapeutically effectiveamount will vary depending upon the subject and disease condition beingtreated, the weight and age of the subject, the severity of the diseasecondition, the particular compound selected from Formula I and FormulaII, the dosing regimen to be followed, timing of administration, themanner of administration and the like, all of which can readily bedetermined by one of ordinary skill in the art.

“ATPase” refers to an enzyme that hydrolyzes ATP. ATPases includeproteins comprising molecular motors such as the myosins.

As used herein, “frailty” is a syndrome characterized by meeting threeof the of the following five attributes: unintentional weight loss,muscle weakness, slow walking speed, exhaustion, and low physicalactivity.

As used herein, “cachexia” means a metabolic defect often associatedwith cancer that is characterized by progressive weight loss due to thedeletion of adipose tissue and skeletal muscle.

As used herein, “muscle spasm” means an involuntary contraction of amuscle. Muscle spasms may lead to cramps.

As used herein, “post-surgical muscle weakness” refers to a reduction inthe strength of one or more muscles following surgical procedure.Weakness may be generalized (i.e. total body weakness) or localized to aspecific area, side of the body, limb, or muscle.

As used herein, “post-traumatic muscle weakness” refers to a reductionin the strength of one or more muscles following a traumatic episode(e.g. bodily injury). Weakness may be generalized (i.e. total bodyweakness) or localized to a specific area, side of the body, limb, ormuscle.

As used herein, “neuromuscular disease” means any disease that affectsany part of the nerve and muscle. Neuromuscular disease encompassescritical illness polyneuropathy, prolonged neuromuscular blockade, acutemyopathy as well as acute inflammatory demyelinatingpolyradiculoneuropathy, amyotrophic lateral sclerosis (ALS), autonomicneuropathy, Charcot-Marie-Tooth disease and other hereditary motor andsensory neuropathies, chronic inflammatory demyelinatingpolyradiculoneuropathy, dermatomyositis/polymyositis, diabeticneuropathy, dystrophinopathies, endocrine myopathies, focal muscularatrophies, hemifacial spasm, hereditary neuropathies of theCharcot-Marie-Tooth disease type, inclusion body myositis, Kennedydisease, Lambert-Eaton myasthenic syndrome, muscular dystrophy (e.g.,limb-girdle, Duchenne, Becker, myotonic, facioscapulohumeral, etc.),metabolic myopathies, metabolic neuropathy, multifocal motor neuropathywith conduction blocks, myasthenia gravis, neuropathy of FriedreichAtaxia, neuropathy of leprosy, nutritional neuropathy, periodicparalyses, primary lateral sclerosis, restrictive lung disease,sarcoidosis and neuropathy, Schwartz-Jampel Syndrome, spinal muscleatrophy, stiff person syndrome, thyroid disease, traumatic peripheralnerve lesions, vasculitic neuropathy, among others.

As used herein “obesity” means having a body mass index (BMI) greaterthan or equal to 30 kg/m². BMI is defined as weight (kg) divided byheight (m²). Obesity encompasses hyperplastic obesity, an increase inthe number of fat cells, and hypertrophic obesity, an increase in thesize of the fat cells. Overweight is defined as having a BMI from 25 upto 30 kg/m²; obesity as a BMI greater than or equal to 30 kg/m², asstated above, and severe (or morbid) obesity is defined as a BMI greaterthan or quality to 40 kg/m².

As used herein, “sarcopenia” means a loss of skeletal muscle mass,quality, and strength. Often sarcopenia is attributed to ageing, but isalso associated with HIV infection. Sarcopenia may lead to frailty, forexample, in the elderly.

As used herein, “wasting syndrome” means a condition characterized byinvoluntary weight loss associated with chronic fever and diarrhea. Insome instances, patients with wasting syndrome lose 10% of baseline bodyweight within one month.

Compounds of Formula I and compounds of Formula II also includecrystalline and amorphous forms of those compounds, including, forexample, polymorphs, pseudopolymorphs, solvates, hydrates, unsolvatedpolymorphs (including anhydrates), conformational polymorphs, andamorphous forms of the compounds, as well as mixtures thereof.“Crystalline form,” “polymorph,” and “novel form” may be usedinterchangeably herein, and are meant to include all crystalline andamorphous forms of the compound, including, for example, polymorphs,pseudopolymorphs, solvates, hydrates, unsolvated polymorphs (includinganhydrates), conformational polymorphs, and amorphous forms, as well asmixtures thereof, unless a particular crystalline or amorphous form isreferred to.

The compounds disclosed herein can be used in different enrichedisotopic forms, e.g., enriched in the content of ²H, ³H, ¹¹C, ¹³C and/or¹⁴C. In one particular embodiment, the compounds are deuterated. Suchdeuterated forms can be made by the procedure described in U.S. Pat.Nos. 5,846,514 and 6,334,997. As described in U.S. Pat. Nos. 5,846,514and 6,334,997, deuteration can improve the efficacy and increase theduration of action of drugs.

Deuterium substituted compounds can be synthesized using various methodssuch as described in: Dean, Dennis C.; Editor. Recent Advances in theSynthesis and Applications of Radiolabeled Compounds for Drug Discoveryand Development. [In: Curr., Pharm. Des., 2000; 6(10)] 2000, 110 pp;Kabalka, George W.; Varma, Rajender S. The Synthesis of RadiolabeledCompounds via Organometallic Intermediates, Tetrahedron, 1989, 45(21),6601-21; and Evans, E. Anthony. Synthesis of radiolabeled compounds, J.Radioanal. Chem., 1981, 64(1-2), 9-32.

Chemical entities include, but are not limited to, compounds of FormulaI, compounds of Formula II, and all pharmaceutically acceptable formsthereof. Pharmaceutically acceptable forms of the compounds recitedherein include pharmaceutically acceptable salts, chelates, non-covalentcomplexes, prodrugs, and mixtures thereof. In certain embodiments, thecompounds described herein are in the form of pharmaceuticallyacceptable salts. Hence, the terms “chemical entity” and “chemicalentities” also encompass pharmaceutically acceptable salts, chelates,non-covalent complexes, prodrugs, and mixtures.

“Pharmaceutically acceptable salts” include, but are not limited tosalts with inorganic acids, such as hydrochlorate, phosphate,diphosphate, hydrobromate, sulfate, sulfinate, nitrate, and like salts;as well as salts with an organic acid, such as malate, maleate,fumarate, tartrate, succinate, citrate, acetate, lactate,methanesulfonate, p-toluenesulfonate, 2-hydroxyethylsulfonate, benzoate,salicylate, stearate, and alkanoate such as acetate, HOOC—(CH₂)_(n)—COOHwhere n ranges from 0 to 4, and like salts. Similarly, pharmaceuticallyacceptable cations include, but are not limited to sodium, potassium,calcium, aluminum, lithium, and ammonium.

In addition, if the compound of Formula I or the compound of Formula IIis obtained as an acid addition salt, the free base can be obtained bybasifying a solution of the acid salt. Conversely, if the product is afree base, an addition salt, particularly a pharmaceutically acceptableaddition salt, may be produced by dissolving the free base in a suitableorganic solvent and treating the solution with an acid, in accordancewith conventional procedures for preparing acid addition salts from basecompounds. Those skilled in the art will recognize various syntheticmethodologies that may be used to prepare non-toxic pharmaceuticallyacceptable addition salts.

As noted above, prodrugs also fall within the scope of chemicalentities, for example, ester or amide derivatives of the compoundsselected from Formula I and Formula II. The term “prodrug” includes anycompound that becomes a compound of Formula I or a compound of FormulaII when administered to a patient, e.g., upon metabolic processing ofthe prodrug. Examples of prodrugs include, but are not limited to,acetate, formate, benzoate, and like derivatives of functional groups(such as alcohol or amine groups) in the compounds selected from FormulaI and Formula II.

The term “chelate” refers to the chemical entity formed by thecoordination of a compound to a metal ion at two (or more) points.

The term “non-covalent complex” refers to the chemical entity formed bythe interaction of a compound and another molecule wherein a covalentbond is not formed between the compound and the molecule. For example,complexation can occur through van der Waals interactions, hydrogenbonding, and electrostatic interactions (also called ionic bonding).

The term “active agent” is used to indicate a chemical entity which hasbiological activity. In certain embodiments, an “active agent” is acompound having pharmaceutical utility.

The term “therapeutically effective amount” of a chemical entity meansan amount effective, when administered to a human or non-human patient,to treat a disease, e.g., a therapeutically effective amount may be anamount sufficient to treat a disease or disorder responsive to myosinactivation. The therapeutically effective amount may be ascertainedexperimentally, for example by assaying blood concentration of thechemical entity, or theoretically, by calculating bioavailability.

By “significant” is meant any detectable change that is statisticallysignificant in a standard parametric test of statistical significancesuch as Student's T-test, where p<0.05.

“Patient” refers to an animal, such as a mammal, for example a human,that has been or will be the object of treatment, observation orexperiment. The methods described herein can be useful in both humantherapy and veterinary applications. In some embodiments, the patient isa mammal, and in some embodiments, the patient is human.

“Treatment” or “treating” means any treatment of a disease in a patient,including:

-   -   (a) preventing the disease, that is, causing the clinical        symptoms of the disease not to develop;    -   (b) inhibiting the disease;    -   (c) slowing or arresting the development of clinical symptoms;        and/or    -   (d) relieving the disease, that is, causing the regression of        clinical symptoms.

As used herein, “modulation” refers to a change in one or more ofskeletal myosin, skeletal actin, skeletal tropomyosin, skeletal troponinC, skeletal troponin I, skeletal troponin T, and skeletal muscle,including fragments and isoforms thereof, as well as the skeletalsarcomere as a direct or indirect response to the presence of at leastone chemical entity described herein, relative to the activity of themyosin or sarcomere in the absence of the compound. The change may be anincrease in activity (potentiation) or a decrease in activity(inhibition), and may be due to the direct interaction of the compoundwith myosin or the sarcomere, or due to the interaction of the compoundwith one or more other factors that in turn effect one or more ofskeletal myosin, skeletal actin, skeletal tropomyosin, skeletal troponinC, skeletal troponin I, skeletal troponin T, and skeletal muscle,including fragments and isoforms thereof, as well as the skeletalsarcomere.

Provided is a method of treating myasthenia gravis in a subjectcomprising administering to the subject at least one chemical entitychosen from compounds of Formula I and compounds of Formula II:

and pharmaceutically acceptable salts thereof, wherein

R₁ and R₄ are independently selected from hydrogen, halo, hydroxy,optionally substituted acyl, optionally substituted alkyl, optionallysubstituted amino, optionally substituted alkenyl, optionallysubstituted alkynyl, optionally substituted cycloalkyl, optionallysubstituted heteroaryl, optionally substituted alkoxy, optionallysubstituted aminocarbonyl, sulfonyl, sulfanyl, sulfinyl, carboxy,optionally substituted alkoxycarbonyl, and cyano; and in thealternative, R₄ and R₁, taken together with any intervening atoms, forma fused ring system selected from optionally substituted fused aryl,optionally substituted fused heteroaryl, optionally substituted fusedcycloalkyl, and optionally substituted fused heterocycloalkyl; and

R₂ is selected from optionally substituted alkyl, optionally substitutedcycloalkyl, optionally substituted aryl, optionally substitutedheteroaryl, and optionally substituted heterocycloalkyl; provided that

R₁ is not hex-1-enyl; and further provided that the compound of FormulaI or the compound of Formula II is not

-   (S)-6-bromo-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   1,5,6-trimethyl-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   1-methyl-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   6-bromo-1-(3-nitrobenzyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   5-(hydroxymethyl)-1,6-dimethyl-1H-imidazo[4,5-b]pyrazin-2(3H)-one;    or-   1-(piperidin-4-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one.

In some embodiments, R₂ is selected from optionally substituted loweralkyl, optionally substituted cycloalkyl, optionally substituted alkoxy,and optionally substituted heterocycloalkyl.

In some embodiments, R₂ is selected from heterocycloalkyl, cycloalkyl,lower alkyl, and lower alkyl substituted with optionally substitutedphenyl, hydroxy, optionally substituted alkoxy, optionally substitutedamino and optionally substituted heterocycloalkyl.

In some embodiments, R₂ is selected from 1-(R)-phenylethyl,1-(S)-phenylethyl, benzyl, 3-pentyl, 4-heptyl,4-methyl-1-morpholinopentan-2-yl isobutyl, cyclohexyl, cyclopropyl,sec-butyl, tert-butyl, isopropyl, 1-hydroxybutan-2-yl,tetrahydro-2H-pyran-4-yl, 1-methoxybutan-2-yl, 1-aminobutan-2-yl, and1-morpholinobutan-2-yl.

In some embodiments, R₁ is selected from hydrogen, halo, acyl,optionally substituted lower alkyl, optionally substituted amino,optionally substituted pyrazolyl, optionally substituted alkenyl,optionally substituted alkynyl, optionally substituted lower alkoxy, and—S-(optionally substituted lower alkyl).

In some embodiments, R₁ is selected from hydrogen, halo, acyl,optionally substituted lower alkyl, dialkylamino, amino substituted withan alkyl group and with a group chosen from acyl, aminocarbonyl,alkoxycarbonyl, and sulfonyl; optionally substituted pyrazolyl,optionally substituted alkenyl, optionally substituted alkynyl,optionally substituted lower alkoxy, and —S-(optionally substitutedlower alkyl).

In some embodiments, R₁ is selected from hydrogen, halo, acyl, alkenyl,alkynyl, lower alkoxy, optionally substituted amino, pyrazolylsubstituted with lower alkyl, —S-(optionally substituted lower alkyl),lower alkyl, and lower alkyl substituted with halo.

In some embodiments, R₁ is selected from hydrogen, halo, acyl, alkenyl,alkynyl, lower alkoxy, dialkylamino, amino substituted with an alkylgroup and with a group chosen from acyl, aminocarbonyl, alkoxycarbonyl,and sulfonyl, pyrazolyl substituted with lower alkyl, —S-(optionallysubstituted lower alkyl), lower alkyl, and lower alkyl substituted withhalo.

In some embodiments, R₁ is selected from hydrogen, bromo, chloro,fluoro, methyl, ethyl, propyl, hexenyl, butenyl, propenyl, vinyl,ethynyl, methoxy, ethoxy, methylsulfanyl, dimethylamino, and methylsubstituted with up to three fluoro groups.

In some embodiments, R₁ is selected from hydrogen, bromo, chloro,fluoro, methyl, ethyl, n-propyl, isopropyl, dimethylamino,isobuten-1-yl, (Z)-propen-1-yl, (E)-propen-1-yl, propen-2-yl, vinyl,ethynyl, methoxy, ethoxy, methylsulfanyl, and trifluoromethyl.

In some embodiments, R₄ is selected from hydrogen, halo, acyl,optionally substituted alkyl, alkenyl, optionally substitutedcycloalkyl, optionally substituted aminocarbonyl, sulfanyl, optionallysubstituted amino, and optionally substituted alkoxycarbonyl.

In some embodiments, R₄ is selected from hydrogen, halo, acyl,optionally substituted lower alkyl, lower alkenyl, optionallysubstituted cycloalkyl, optionally substituted aminocarbonyl, sulfanyl,optionally substituted amino, and optionally substituted loweralkoxycarbonyl.

In some embodiments, R₄ is selected from hydrogen, halo, acyl, loweralkyl, lower alkenyl, cycloalkyl, optionally substituted aminocarbonyl,sulfanyl, and lower alkoxycarbonyl.

In some embodiments, R₄ is selected from hydrogen, bromo, chloro,fluoro, acetyl, methyl, ethyl, vinyl, cyclohexen-1-yl, methylcarbamoyl,dimethylcarbamoyl, methylsulfanyl, and methoxycarbonyl.

In some embodiments, R₄ is hydrogen.

In some embodiments, R₄ and R₁, taken together with any interveningatoms, form a fused ring system selected from optionally substitutedfused aryl, optionally substituted fused cycloalkyl, and optionallysubstituted fused heterocycloalkyl.

In some embodiments, R₄ and R₁ are taken together to form an optionallysubstituted benzo group.

In some embodiments, R₄ and R₁ are taken together to form a benzo group.

In some embodiments, the compound of Formula I is chosen from

-   1-((1R)-1-methyl-2-morpholin-4-ylethyl)-6-bromoimidazo[4,5-b]pyrazin-2-ol;-   1-(ethylpropyl)-6-ethynylimidazo[4,5-b]pyrazin-2-ol;-   1-(ethylpropyl)-6-methoxyimidazo[4,5-b]pyrazin-2-ol;-   1-(1,1-dimethyl-2-morpholin-4-ylethyl)-6-bromoimidazo[4,5-b]pyrazin-2-ol;-   6-(1H-1,2,3-triazol-4-yl)-1-(ethylpropyl)imidazo[4,5-b]pyrazin-2-ol;-   1-(ethylpropyl)-6-(trifluoromethypimidazo[4,5-b]pyrazin-2-ol;-   1-[(1R)-1-(morpholin-4-ylmethyl)propyl]-6-ethynylimidazo[4,5-b]pyrazin-2-ol;-   1-(ethylpropyl)-6-{2-[1-(ethylpropyl)-2-hydroxyimidazo[4,5-e]pyrazin-6-yl]ethynyl}imidazo[4,5-b]pyrazin-2-ol;-   6-(dimethylamino)-1-(ethylpropyl)imidazo[4,5-b]pyrazin-2-ol;-   6-ethyl-1-(ethylpropyl)imidazo[4,5-b]pyrazin-2-ol;-   (E)-1-(pentan-3-yl)-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   (E)-1-cyclohexyl-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   (E)-1-cyclopropyl-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   (E)-1-isopropyl-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   (E)-6-(prop-1-enyl)-1-(tetrahydro-2H-pyran-4-yl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   (R)-6-(methylthio)-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   (R)-6-bromo-1-(1-hydroxybutan-2-yl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   (R)-6-bromo-1-(1-morpholinobutan-2-yl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   (R)-6-bromo-1-(1-morpholinopropan-2-yl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   (R)-6-bromo-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   (R)-6-bromo-1-sec-butyl-1H-imidazo[4,5-b]pyrazin-2-ol;-   (S)-(2-hydroxy-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-6-yl)(4-methylpiperazin-1-yl)methanone;-   (S)-(2-hydroxy-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-6-yl)(morpholino)methanone;-   (S)-(2-hydroxy-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-6-yl)(piperidin-1-yl)methanone;-   (S)-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   (S)-1-(1-phenylethyl)-1H-imidazo[4,5-b]quinoxalin-2-ol;-   (S)-1-(1-phenylethyl)-6-(piperidin-1-ylmethyl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   (S)-1-(1-phenylethyl)-6-propyl-1H-imidazo[4,5-b]pyrazin-2-ol;-   (S)-1-(1-phenylethyl)-6-vinyl-1H-imidazo[4,5-b]pyrazin-2-ol;-   (S)-1-(2-hydroxy-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-6-yl)ethanone;-   (S)-2-hydroxy-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazine-6-carbonitrile;-   (S)-2-hydroxy-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazine-6-carboxamide;-   (S)-2-hydroxy-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazine-6-carboxylic    acid;-   (S)-2-hydroxy-N,N-dimethyl-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazine-6-carboxamide;-   (S)-2-hydroxy-N-methyl-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazine-6-carboxamide;-   (S)-6-((4-methylpiperazin-1-yl)methyl)-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   (S)-6-((dimethylamino)methyl)-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   (S)-6-(2-hydroxypropan-2-yl)-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   (S)-6-(2-methylprop-1-enyl)-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   (S)-6-(methylsulfonyl)-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   (S)-6-(methylthio)-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   (S)-6-(morpholinomethyl)-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   (S)-6-bromo-1-(1-hydroxybutan-2-yl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   (S)-6-bromo-1-(1-morpholinobutan-2-yl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   (S)-6-bromo-1-(1-morpholinopropan-2-yl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   (S)-6-bromo-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   (S)-6-bromo-1-sec-butyl-1H-imidazo[4,5-b]pyrazin-2-ol;-   (S)-6-cyclohexenyl-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   (S)-6-cyclohexyl-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   (S)-6-ethoxy-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   (S)-6-ethyl-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   (S)-6-hexyl-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   (S)-6-isobutyl-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   (S)-6-methoxy-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   (S)-methyl    2-hydroxy-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazine-6-carboxylate;-   (S)—N,N-diethyl-2-hydroxy-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazine-6-carboxamide;-   (S)—N-benzyl-2-hydroxy-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazine-6-carboxamide;-   (S,E)-1-(1-phenylethyl)-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   (S,Z)-1-(1-phenylethyl)-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   (S,Z)-6-(hex-2-enyl)-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   (Z)-1-(pentan-3-yl)-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   (Z)-1-cyclohexyl-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   (Z)-1-cyclopropyl-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   (Z)-1-isopropyl-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   (Z)-6-(prop-1-enyl)-1-(tetrahydro-2H-pyran-4-yl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   1-(1-aminobutan-2-yl)-6-bromo-1H-imidazo[4,5-b]pyrazin-2-ol;-   1-(1-morpholinobutan-2-yl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   1-(2-hydroxy-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-5-yl)ethanone;-   1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazine-2,6-diol;-   1-(pentan-3-yl)-1H-imidazo[4,5-b]quinoxalin-2-ol;-   1-(pentan-3-yl)-5-vinyl-1H-imidazo[4,5-b]pyrazin-2-ol;-   1-(pentan-3-yl)-6-(prop-1-ynyl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   1-(pentan-3-yl)-6-(trifluoromethyl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   1-benzyl-6-(methylthio)-1H-imidazo[4,5-b]pyrazin-2-ol;-   1-benzyl-6-bromo-1H-imidazo[4,5-b]pyrazin-2-ol;-   1-cyclohexyl-6-(methylthio)-1H-imidazo[4,5-b]pyrazin-2-ol;-   1-cyclopropyl-6-(methylthio)-1H-imidazo[4,5-b]pyrazin-2-ol;-   1-isopropyl-6-(methylthio)-1H-imidazo[4,5-b]pyrazin-2-ol;-   2-(6-bromo-2-hydroxy-1H-imidazo[4,5-b]pyrazin-1-yl)-1-morpholinobutan-1-one;-   2-(6-bromo-2-hydroxy-1H-imidazo[4,5-b]pyrazin-1-yl)butanoic acid;-   2-(6-bromo-2-hydroxy-1H-imidazo[4,5-b]pyrazin-1-yl)propane-1,3-diol;-   2-hydroxy-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazine-5-carboxylic    acid;-   2-hydroxy-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazine-6-carbonitrile;-   2-hydroxy-N,N-dimethyl-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazine-5-carboxamide;-   2-hydroxy-N-methyl-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazine-5-carboxamide;-   5-(methylthio)-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   5-bromo-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   5-ethyl-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   6-(methylsulfinyl)-1-((S)-1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   6-(methylthio)-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   6-(methylthio)-1-(tetrahydro-2H-pyran-4-yl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   6-bromo-1-(1-(4-(methylsulfonyl)piperazin-1-yl)butan-2-yl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   6-bromo-1-(1-(4-methylpiperazin-1-yl)butan-2-yl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   6-bromo-1-(1-(dimethylamino)butan-2-yl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   6-bromo-1-(1-(methylamino)butan-2-yl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   6-bromo-1-(1-methoxybutan-2-yl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   6-bromo-1-(2-methyl-1-morpholinopropan-2-yl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   6-bromo-1-(2-morpholinoethyl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   6-bromo-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   6-bromo-1-(tetrahydro-2H-pyran-4-yl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   6-bromo-1-cyclohexyl-1H-imidazo[4,5-b]pyrazin-2-ol;-   6-bromo-1-cyclopropyl-1H-imidazo[4,5-b]pyrazin-2-ol;-   6-bromo-1-isopropyl-1H-imidazo[4,5-b]pyrazin-2-ol;-   6-bromo-1-tert-butyl-1H-imidazo[4,5-b]pyrazin-2-ol;-   6-cyclopropyl-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   6-ethynyl-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   6-methoxy-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   6-methyl-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2-ol;-   methyl    2-hydroxy-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazine-5-carboxylate;-   methyl    4-(2-(6-bromo-2-hydroxy-1H-imidazo[4,5-b]pyrazin-1-yl)butyl)piperazine-1-carboxylate;-   1-(ethylpropyl)-6-(1-methylpyrazol-4-yl)imidazo[4,5-b]pyrazin-2-ol;-   6-bromo-1-(propylbutyl)imidazo[4,5-b]pyrazin-2-ol;-   1-[(1R)-3-methyl-1-(morpholin-4-ylmethyl)butyl]-6-bromoimidazo[4,5-b]pyrazin-2-ol;-   1-(ethylpropyl)-6-vinylimidazo[4,5-b]pyrazin-2-ol;-   1-(ethylpropyl)-6-(1-methylvinyl)imidazo[4,5-b]pyrazin-2-ol;-   1-(ethylpropyl)-6-(methylethyl)imidazo[4,5-b]pyrazin-2-ol;-   6-chloro-1-(ethylpropyl)imidazo[4,5-b]pyrazin-2-ol; and-   6-(dimethylamino)-1-(ethylpropyl)imidazo[4,5-b]pyrazin-2-ol.

In some embodiments, the compound of Formula II is chosen from thefollowing tautomers of compounds of Formula I:

-   (R)-6-bromo-1-(1-morpholinopropan-2-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   6-ethynyl-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   6-methoxy-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   6-bromo-1-(2-methyl-1-morpholinopropan-2-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   1-(pentan-3-yl)-6-(1H-1,2,3-triazol-4-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   1-(pentan-3-yl)-6-(trifluoromethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (R)-6-ethynyl-1-(1-morpholinobutan-2-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   6-((2-hydroxy-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-6-yl)ethynyl)-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   6-(dimethylamino)-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   6-ethyl-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (E)-1-(pentan-3-yl)-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (E)-1-cyclohexyl-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (E)-1-cyclopropyl-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (E)-1-isopropyl-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (E)-6-(prop-1-enyl)-1-(tetrahydro-2H-pyran-4-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (R)-6-(methylthio)-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (R)-6-bromo-1-(1-hydroxybutan-2-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (R)-6-bromo-1-(1-morpholinobutan-2-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (R)-6-bromo-1-(1-morpholinopropan-2-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (R)-6-bromo-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (R)-6-bromo-1-sec-butyl-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (S)-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (S)-1-(1-phenylethyl)-1H-imidazo[4,5-b]quinoxalin-2(3H)-one;-   (S)-1-(1-phenylethyl)-6-(piperidin-1-ylmethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (S)-1-(1-phenylethyl)-6-(piperidine-1-carbonyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (S)-1-(1-phenylethyl)-6-propyl-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (S)-1-(1-phenylethyl)-6-vinyl-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (S)-2-oxo-3-(1-phenylethyl)-2,3-dihydro-1H-imidazo[4,5-b]pyrazine-5-carbonitrile;-   (S)-2-oxo-3-(1-phenylethyl)-2,3-dihydro-1H-imidazo[4,5-b]pyrazine-5-carboxamide;-   (S)-2-oxo-3-(1-phenylethyl)-2,3-dihydro-1H-imidazo[4,5-b]pyrazine-5-carboxylic    acid;-   (S)-6-((4-methylpiperazin-1-yl)methyl)-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (S)-6-((dimethylamino)methyl)-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (S)-6-(2-hydroxypropan-2-yl)-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (S)-6-(2-methylprop-1-enyl)-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (S)-6-(4-methylpiperazine-1-carbonyl)-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (S)-6-(methylsulfonyl)-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (S)-6-(methylthio)-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (S)-6-(morpholine-4-carbonyl)-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (S)-6-(morpholinomethyl)-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (S)-6-acetyl-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (S)-6-bromo-1-(1-hydroxybutan-2-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (S)-6-bromo-1-(1-morpholinobutan-2-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (S)-6-bromo-1-(1-morpholinopropan-2-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (S)-6-bromo-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (S)-6-bromo-1-sec-butyl-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (S)-6-cyclohexenyl-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (S)-6-cyclohexyl-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (S)-6-ethoxy-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (S)-6-ethyl-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (S)-6-hexyl-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (S)-6-isobutyl-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (S)-6-methoxy-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (S)-methyl    2-oxo-3-(1-phenylethyl)-2,3-dihydro-1H-imidazo[4,5-b]pyrazine-5-carboxylate;-   (S)—N,N-diethyl-2-oxo-3-(1-phenylethyl)-2,3-dihydro-1H-imidazo[4,5-b]pyrazine-5-carboxamide;-   (S)—N,N-dimethyl-2-oxo-3-(1-phenylethyl)-2,3-dihydro-1H-imidazo[4,5-b]pyrazine-5-carboxamide;-   (S)—N-benzyl-2-oxo-3-(1-phenylethyl)-2,3-dihydro-1H-imidazo[4,5-b]pyrazine-5-carboxamide;-   (S)—N-methyl-2-oxo-3-(1-phenylethyl)-2,3-dihydro-1H-imidazo[4,5-b]pyrazine-5-carboxamide;-   (S,E)-1-(1-phenylethyl)-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (S,Z)-1-(1-phenylethyl)-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (S,Z)-6-(hex-2-enyl)-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (Z)-1-(pentan-3-yl)-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (Z)-1-cyclohexyl-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (Z)-1-cyclopropyl-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (Z)-1-isopropyl-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (Z)-6-(prop-1-enyl)-1-(tetrahydro-2H-pyran-4-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   1-(1-aminobutan-2-yl)-6-bromo-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   1-(1-morpholinobutan-2-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   1-(pentan-3-yl)-1H-imidazo[4,5-b]quinoxalin-2(3H)-one;-   1-(pentan-3-yl)-5-vinyl-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   1-(pentan-3-yl)-6-(prop-1-ynyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   1-(pentan-3-yl)-6-(trifluoromethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   1-benzyl-6-(methylthio)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   1-benzyl-6-bromo-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   1-cyclohexyl-6-(methylthio)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   1-cyclopropyl-6-(methylthio)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   1-isopropyl-6-(methylthio)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   2-(6-bromo-2-oxo-2,3-dihydro-1H-imidazo[4,5-b]pyrazin-1-yl)butanoic    acid;-   2-oxo-1-(pentan-3-yl)-2,3-dihydro-1H-imidazo[4,5-b]pyrazine-5-carboxylic    acid;-   2-oxo-3-(pentan-3-yl)-2,3-dihydro-1H-imidazo[4,5-b]pyrazine-5-carbonitrile;-   5-(methylthio)-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   5-acetyl-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   5-bromo-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   5-ethyl-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   6-(methylsulfinyl)-1-((S)-1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   6-(methylthio)-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   6-(methylthio)-1-(tetrahydro-2H-pyran-4-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   6-bromo-1-(1-(4-(methylsulfonyl)piperazin-1-yl)butan-2-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   6-bromo-1-(1-(4-methylpiperazin-1-yl)butan-2-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   6-bromo-1-(1-(dimethylamino)butan-2-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   6-bromo-1-(1-(methylamino)butan-2-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   6-bromo-1-(1,3-dihydroxypropan-2-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   6-bromo-1-(1-methoxybutan-2-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   6-bromo-1-(1-morpholino-1-oxobutan-2-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   6-bromo-1-(2-methyl-1-morpholinopropan-2-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   6-bromo-1-(2-morpholinoethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   6-bromo-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   6-bromo-1-(tetrahydro-2H-pyran-4-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   6-bromo-1-cyclohexyl-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   6-bromo-1-cyclopropyl-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   6-bromo-1-isopropyl-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   6-bromo-1-tert-butyl-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   6-cyclopropyl-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   6-ethynyl-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   6-hydroxy-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   6-methoxy-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   6-methyl-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   methyl    2-oxo-1-(pentan-3-yl)-2,3-dihydro-1H-imidazo[4,5-b]pyrazine-5-carboxylate;-   methyl    4-(2-(6-bromo-2-oxo-2,3-dihydro-1H-imidazo[4,5-b]pyrazin-1-yl)butyl)piperazine-1-carboxylate;-   N,N-dimethyl-2-oxo-1-(pentan-3-yl)-2,3-dihydro-1H-imidazo[4,5-b]pyrazine-5-carboxamide;-   N-methyl-2-oxo-1-(pentan-3-yl)-2,3-dihydro-1H-imidazo[4,5-b]pyrazine-5-carboxamide;-   6-(1-methyl-1H-pyrazol-4-yl)-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   6-bromo-1-(heptan-4-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   (R)-6-bromo-1-(4-methyl-1-morpholinopentan-2-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   1-(pentan-3-yl)-6-vinyl-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   1-(pentan-3-yl)-6-(prop-1-en-2-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   6-isopropyl-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;-   6-chloro-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one; and-   6-(dimethylamino)-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one.

Also provided is a method of treating myasthenia gravis in a subjectcomprising administering to the subject an effective amount of at leastone chemical entity chosen from compounds of Formula I and compounds ofFormula II:

and pharmaceutically acceptable salts thereof, wherein R₁ is selectedfrom alkenyl and alkynyl; R₄ is hydrogen; and R₂ is selected from3-pentyl, 4-heptyl, 4-methyl-1-morpholinopentan-2-yl isobutyl,cyclohexyl, cyclopropyl, sec-butyl, tert-butyl, isopropyl,1-hydroxybutan-2-yl, tetrahydro-2H-pyran-4-yl, 1-methoxybutan-2-yl,1-aminobutan-2-yl, and 1-morpholinobutan-2-yl; provided that R₁ is nothex-1-enyl.

In some embodiments, R₁ is selected from butenyl, propenyl, vinyl, andethynyl. In certain embodiments, R₁ is selected from isobuten-1-yl,(Z)-propen-1-yl, (E)-propen-1-yl, propen-2-yl, vinyl, and ethynyl.

In some embodiments, R₂ is selected from 3-pentyl, 4-heptyl,4-methyl-1-morpholinopentan-2-yl, isobutyl, sec-butyl, tert-butyl,isopropyl, 1-hydroxybutan-2-yl, tetrahydro-2H-pyran-4-yl,1-methoxybutan-2-yl, 1-aminobutan-2-yl, and 1-morpholinobutan-2-yl. Incertain embodiments, R₂ is selected from 3-pentyl, 4-heptyl, isobutyl,sec-butyl, tert-butyl, isopropyl, and 1-hydroxybutan-2-yl. In stillother embodiments, R₂ is selected from 3-pentyl, 4-heptyl, isobutyl,sec-butyl, tert-butyl, and isopropyl. In certain of these embodiments,R₁ is ethynyl.

In some embodiments, the compound of Formula I is chosen from:1-(ethylpropyl)-6-ethynylimidazo[4,5-b]pyrazin-2-ol;1-[(1R)-1-(morpholin-4-ylmethyl)propyl]-6-ethynylimidazo[4,5-b]pyrazin-2-ol;(E)-1-(pentan-3-yl)-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2-ol;(E)-1-(pentan-3-yl)-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2-ol;(E)-1-cyclohexyl-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2-ol;(E)-1-cyclopropyl-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2-ol;(E)-1-isopropyl-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2-ol;(E)-6-(prop-1-enyl)-1-(tetrahydro-2H-pyran-4-yl)-1H-imidazo[4,5-b]pyrazin-2-ol;(Z)-1-(pentan-3-yl)-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2-ol;(Z)-1-cyclohexyl-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2-ol;(Z)-1-cyclopropyl-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2-ol;(Z)-1-isopropyl-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2-ol;(Z)-6-(prop-1-enyl)-1-(tetrahydro-2H-pyran-4-yl)-1H-imidazo[4,5-b]pyrazin-2-ol;1-(pentan-3-yl)-6-(prop-1-ynyl)-1H-imidazo[4,5-b]pyrazin-2-ol;6-ethynyl-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2-ol;1-(ethylpropyl)-6-vinylimidazo[4,5-b]pyrazin-2-ol; and1-(ethylpropyl)-6-(1-methylvinyl)imidazo[4,5-b]pyrazin-2-ol; andpharmaceutically acceptable salts thereof. In certain embodiments, thecompound of Formula I is1-(ethylpropyl)-6-ethynylimidazo[4,5-b]pyrazin-2-ol or6-ethynyl-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2-ol, or apharmaceutically acceptable salt thereof.

In some embodiments, the compound of Formula II is chosen from6-ethynyl-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;(R)-6-ethynyl-1-(1-morpholinobutan-2-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;(E)-1-(pentan-3-yl)-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;(E)-1-cyclohexyl-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;(E)-1-cyclopropyl-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;(E)-1-isopropyl-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;(E)-6-(prop-1-enyl)-1-(tetrahydro-2H-pyran-4-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;(Z)-1-(pentan-3-yl)-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;(Z)-1-cyclohexyl-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;(Z)-1-cyclopropyl-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;(Z)-1-isopropyl-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;(Z)-6-(prop-1-enyl)-1-(tetrahydro-2H-pyran-4-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;1-(pentan-3-yl)-6-(prop-1-ynyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;1-(pentan-3-yl)-6-vinyl-1H-imidazo[4,5-b]pyrazin-2(3H)-one; and1-(pentan-3-yl)-6-(prop-1-en-2-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one;and pharmaceutically acceptable salts thereof. In some embodiments, thecompound of Formula II is6-ethynyl-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one or apharmaceutically acceptable salt thereof.

In some embodiments, the patient is administered a pharmaceuticallyacceptable composition comprising a pharmaceutically acceptable carrierand at least one chemical entity described herein. In certainembodiments, the chemical entity is1-(ethylpropyl)-6-ethynylimidazo[4,5-b]pyrazin-2-ol or6-ethynyl-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2-ol, or apharmaceutically acceptable salt thereof, or6-ethynyl-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one or apharmaceutically acceptable salt thereof.

Also provided is a method of decreasing muscle fatigue, or slowing therate of muscle fatigue, in a patient suffering from myasthenia gravis,comprising administering to the patient at least one compound of FormulaI or Formula II, or a pharmaceutically acceptable salt thereof, or apharmaceutically acceptable composition comprising a pharmaceuticallyacceptable carrier and at least one compound of Formula I or Formula II,or a pharmaceutically acceptable salt thereof. In certain embodiments,the compound of Formula I is1-(ethylpropyl)-6-ethynylimidazo[4,5-b]pyrazin-2-ol or6-ethynyl-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2-ol, or apharmaceutically acceptable salt thereof. In some embodiments, thecompound of Formula II is6-ethynyl-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one or apharmaceutically acceptable salt thereof.

Also provided is a method of increasing muscle force and/or power in apatient suffering from myasthenia gravis, comprising administering tothe patient at least one compound of Formula I or Formula II, or apharmaceutically acceptable salt thereof, or a pharmaceuticallyacceptable composition comprising a pharmaceutically acceptable carrierand at least one compound of Formula I or Formula II, or apharmaceutically acceptable salt thereof. In certain embodiments, thecompound of Formula I is1-(ethylpropyl)-6-ethynylimidazo[4,5-b]pyrazin-2-ol or6-ethynyl-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2-ol, or apharmaceutically acceptable salt thereof. In some embodiments, thecompound of Formula II is6-ethynyl-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one or apharmaceutically acceptable salt thereof.

The compounds of Formula I can be named and numbered (e.g., usingNamExpert™ available from Cheminnovation or the automatic naming featureof Chem Draw Ultra version 10.0 from Cambridge Soft Corporation) asdescribed below. For example, the compound:

i.e., the compound according to Formula I where R₁ is (E)-propen-1yl, R₂is (S)-sec-phenethyl, and R₄ is H, can be named(S,E)-1-(1-phenylethyl)-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2-ol.

Likewise the compound:

i.e., the compound according to Formula I where R₁ is (Z)-propen-1-yl,R₂ is 3-pentyl, and R₄ is H, can be named(Z)-1-(pentan-3-yl)-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2-ol.

Likewise, the compound:

i.e., the compound according to Formula I where R₁ is ethynyl, R₂ is3-pentyl, and R₄ is H, can be named either1-(ethylpropyl)-6-ethynylimidazo[4,5-b]pyrazin-2-ol or6-ethynyl-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2-ol.

Similarly, the compounds of Formula II can be named and numbered (e.g.,using NamExpert™ available from Cheminnovation or the automatic namingfeature of Chem Draw Ultra version 10.0 from Cambridge Soft Corporation)as described below. For example, the compound:

i.e., the compound according to Formula II where R₁ is (E)-propen-1-yl,R₂ is (S)-sec-phenethyl, and R₄ is H, can be named(S,E)-1-(1-phenylethyl)-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one.

Likewise the compound:

i.e., the compound according to Formula II where R₁ is (Z)-propen-1-yl,R₂ is 3-pentyl, and R₄ is H, can be named(Z)-1-(pentan-3-yl)-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one.

The chemical entities described herein can be synthesized utilizingtechniques well known in the art, e.g., as illustrated below withreference to the Reaction Schemes.

Unless specified to the contrary, the reactions described herein takeplace at atmospheric pressure, generally within a temperature range from−10° C. to 200° C. Further, except as employed in the Examples or asotherwise specified, reaction times and conditions are intended to beapproximate, e.g., taking place at about atmospheric pressure within atemperature range of about −10° C. to about 110° C. over a period ofabout 1 to about 24 hours; reactions left to run overnight average aperiod of about 16 hours.

The terms “solvent,” “organic solvent,” and “inert solvent” each mean asolvent inert under the conditions of the reaction being described inconjunction therewith [including, for example, benzene, toluene,acetonitrile, tetrahydrofuran (“THF”), dimethylformamide (“DMF”),chloroform, methylene chloride (or dichloromethane), diethyl ether,methanol, N-methylpyrrolidone (“NMP”), pyridine and the like]. Unlessspecified to the contrary, the solvents used in the reactions describedherein are inert organic solvents. Unless specified to the contrary, foreach gram of the limiting reagent, one cc (or mL) of solvent constitutesa volume equivalent

Isolation and purification of the chemical entities and intermediatesdescribed herein can be effected, if desired, by any suitable separationor purification procedure such as, for example, filtration, extraction,crystallization, column chromatography, thin-layer chromatography orthick-layer chromatography, or a combination of these procedures.Specific illustrations of suitable separation and isolation procedurescan be had by reference to the examples hereinbelow. However, otherequivalent separation or isolation procedures can also be used.

When desired, the (R)- and (S)-isomers may be resolved by methods knownto those skilled in the art, for example by formation ofdiastereoisomeric salts or complexes which may be separated, forexample, by crystallization; via formation of diastereoisomericderivatives which may be separated, for example, by crystallization,gas-liquid or liquid chromatography; selective reaction of oneenantiomer with an enantiomer-specific reagent, for example enzymaticoxidation or reduction, followed by separation of the modified andunmodified enantiomers; or gas-liquid or liquid chromatography in achiral environment, for example on a chiral support, such as silica witha bound chiral ligand or in the presence of a chiral solvent.Alternatively, a specific enantiomer may be synthesized by asymmetricsynthesis using optically active reagents, substrates, catalysts orsolvents, or by converting one enantiomer to the other by asymmetrictransformation.

Many of the optionally substituted starting compounds and otherreactants are commercially available, e.g., from Aldrich ChemicalCompany (Milwaukee, Wis.) or can be readily prepared by those skilled inthe art using commonly employed synthetic methodology.

Referring to Reaction Scheme 1, Step 1, to a compound of Formula 101,wherein X is halo, is added an excess (such as about 2 to 20equivalents) of a compound of formula R₂—NH₂. The reaction vessel isheated to about 110° C. to 190° C. over about 20 to 40 minutes,optionally with microwave irradiation. The product, a compound ofFormula 102, is isolated and optionally purified.

Referring to Reaction Scheme 1, Step 2, to a solution of a compound ofFormula 102 in a suitable solvent (such as THF) is added a di-activatedcarbonyl equivalent such as carbonyl diimidazole (CDI), phospgene, ortriphosgene. The product, a compound of Formula 103, is isolated andoptionally purified.

Reaction Scheme 2 illustrates reactions for further converting compoundsof Formula 201, wherein X is a leaving group, to compounds of Formula104 through one of Steps 3(a-e). In some embodiments, X is halo, forexample, bromo.

Referring to Reaction Scheme 2, Step 3(a), a compound of Formula 201 andabout 0.05 to 0.15 equivalents of a suitable catalyst such as (Ph₃P)₄Pdin a suitable solvent such as NMP or dioxane, a suitable base, and anexcess (such as about 1.5 to 32 molar equivalents) of a suitable tinreagent such as R₁Sn(butyl)₃ is mixed at from about 0 to about 200° C.for about 6 to 48 hours. The product, a compound of Formula 104 whereinR₁ is selected from optionally substituted alkyl, optionally substitutedalkenyl, optionally substituted alkynyl, and optionally substitutedcycloalkyl, is isolated and optionally purified.

Referring to Reaction Scheme 2, Step 3(b), a compound of Formula 201 andan excess (such as about 4 to 5 equivalents) of a compound of theformula NaSR_(x) where SR_(X) is R₁, and a suitable solvent (such asNMP) is heated to about 50° C. to 200° C. over about 10 min to 24 h,optionally with microwave irradiation. The product, a compound ofFormula 104 wherein R₁ is sulfanyl, is isolated and optionally purified.

Referring to Reaction Scheme 2, Step 3(c), a compound of Formula 201, anexcess (such as about 1.9 to 2.3 equivalents) of a compound of theformula R₁B(OH)₂, about 0.10 to 0.15 equivalents of (DPPF)PdCl₂, asuitable solvent (such as dioxane) and about 2 to 3 equivalents of asuitable base (such as 2N K₂CO₃) is heated to about 90° C. for about 6to 24 hours. The product, a compound of Formula 104 wherein R₁ isselected from optionally substituted alkyl, optionally substitutedalkenyl, optionally substituted alkynyl, and optionally substitutedcycloalkyl, is isolated and optionally purified.

Referring to Reaction Scheme 2, Step 3(d), about 2 equivalents ofR_(x)OH where OR_(x) is R₁ and a suitable solvent (such as NMP), andabout 2 equivalents of suitable base (such as NaH) is added followed bya compound of Formula 201. The mixture is heated to about 50 to about200° C. for about 10 minutes to about 48 hours. In some embodiments, thereaction is heated for about 30 minutes, optionally with microwaveirradiation. The product, a compound of Formula 104 wherein R₁ isoptionally substituted alkoxy, is isolated and optionally purified.

Referring to Reaction Scheme 2, Step(e), a compound of Formula 201, anexcess (such as about 2.0 equivalents) of a compound of the formulaKR₁BF₃, an excess (such as about 3 equivalents) of a suitable base (suchas Cs₂CO₃), a suitable amount of (DPPF)PdCl₂ (such as about 0.2equivalents), a suitable solvent (such as dioxane and water) is mixed atabout room temperature to about 100° C. for about 8 to 48 hours and theproduct, a compound of Formula 104 wherein R₁ is selected fromoptionally substituted alkyl, optionally substituted alkenyl, optionallysubstituted alkynyl, and optionally substituted cycloalkyl, is isolatedand optionally purified.

A racemic mixture is optionally placed on a chromatography column andseparated into (R)- and (S)-enantiomers.

The compounds described herein are optionally contacted with apharmaceutically acceptable acid to form the corresponding acid additionsalts.

Pharmaceutically acceptable acid addition salts of compounds of FormulaI or compounds of Formula II are optionally contacted with a base toform the corresponding free base.

The chemical entities described herein modulate one or more of skeletalmyosin, skeletal actin, skeletal tropomyosin, skeletal troponin C,skeletal troponin I, skeletal troponin T, and skeletal muscle, includingfragments and isoforms thereof, as well as the skeletal sarcomere, andare useful to bind to, inhibit and/or potentiate the activity thereof.As used in this context, “modulate” means either increasing ordecreasing myosin activity, whereas “potentiate” means to increaseactivity and “inhibit” means to decrease activity.

The chemical entities, pharmaceutical compositions and methods describedherein are used to treat obesity, sarcopenia, wasting syndrome, frailty,cachexia, muscle spasm, post-surgical and post-traumatic muscleweakness, neuromuscular disease, and other indications in a mammal.

Methods to identify the chemical entities as binding to a protein or asa modulator of the binding characteristics or biological activity of aprotein are described in, for example, U.S. Pat. No. 6,410,254 and U.S.patent application Ser. No. 10/987,165.

For example, test compounds can be assayed in a highly parallel fashionby using multiwell plates by placing the compounds either individuallyin wells or testing them in mixtures. Assay components including thetarget protein complex, coupling enzymes and substrates, and ATP canthen be added to the wells and the absorbance or fluorescence of eachwell of the plate can be measured with a plate reader.

In some embodiments, the method uses a 384 well plate format and a 25 μLreaction volume. A pyruvate kinase/lactate dehydrogenase coupled enzymesystem (Huang T G and Hackney D D. (1994) J Biol Chem 269(23):16493-501)can be used to measure the rate of ATP hydrolysis in each well. As willbe appreciated by those in the art, the assay components are added inbuffers and reagents. The incubation periods can be optimized to giveadequate detection signals over the background. The assay can be done inreal time giving the kinetics of ATP hydrolysis which increases thesignal to noise ratio of the assay.

The compounds can be further tested using skinned muscle fiberpreparations. Such assays are known in the art. See, e.g., Cheung et al.(2002) Nature Cell Biol. 4:83 and U.S. Patent Publication No.20020006962.

The chemical entities described herein are administered at atherapeutically effective dosage, e.g., a dosage sufficient to providetreatment for the disease states previously described. While humandosage levels have yet to be optimized for the chemical entitiesdescribed herein, generally, a daily dose ranges from about 0.05 to 100mg/kg of body weight; in certain embodiments, from about 0.10 to 10.0mg/kg of body weight, and in certain embodiments, from about 0.15 to 1.0mg/kg of body weight. Thus, for administration to a 70 kg person, incertain embodiments, the dosage range would be about from 3.5 to 7000 mgper day; in certain embodiments, about from 7.0 to 700.0 mg per day, andin certain embodiments, about from 10.0 to 100.0 mg per day. The amountof the chemical entity administered will, of course, be dependent on thesubject and disease state being treated, the severity of the affliction,the manner and schedule of administration and the judgment of theprescribing physician; for example, a likely dose range for oraladministration would be from about 70 to 700 mg per day, whereas forintravenous administration a likely dose range would be from about 70 to700 mg per day depending on compound pharmacokinetics.

Administration of the chemical entities described herein can be via anyof the accepted modes of administration for agents that serve similarutilities including, but not limited to, orally, sublingually,subcutaneously, intravenously, intranasally, topically, transdermally,intraperitoneally, intramuscularly, intrapulmonarilly, vaginally,rectally, or intraocularly. In some embodiments, oral or parenteraladministration is used.

Pharmaceutically acceptable compositions include solid, semi-solid,liquid and aerosol dosage forms, such as, e.g., tablets, capsules,powders, liquids, suspensions, suppositories, aerosols or the like. Thechemical entities can also be administered in sustained or controlledrelease dosage forms, including depot injections, osmotic pumps, pills,transdermal (including electrotransport) patches, and the like, forprolonged and/or timed, pulsed administration at a predetermined rate.In certain embodiments, the compositions are provided in unit dosageforms suitable for single administration of a precise dose.

The chemical entities described herein can be administered either aloneor more typically in combination with a conventional pharmaceuticalcarrier, excipient or the like (e.g., mannitol, lactose, starch,magnesium stearate, sodium saccharine, talcum, cellulose, sodiumcrosscarmellose, glucose, gelatin, sucrose, magnesium carbonate, and thelike). If desired, the pharmaceutical composition can also contain minoramounts of nontoxic auxiliary substances such as wetting agents,emulsifying agents, solubilizing agents, pH buffering agents and thelike (e.g., sodium acetate, sodium citrate, cyclodextrine derivatives,sorbitan monolaurate, triethanolamine acetate, triethanolamine oleate,and the like). Generally, depending on the intended mode ofadministration, the pharmaceutical composition will contain about 0.005%to 95%; in certain embodiments, about 0.5% to 50% by weight of achemical entity. Actual methods of preparing such dosage forms areknown, or will be apparent, to those skilled in this art; for example,see Remington's Pharmaceutical Sciences, Mack Publishing Company,Easton, Pa.

In addition, the chemical entities described herein can beco-administered with, and the pharmaceutical compositions can include,other medicinal agents, pharmaceutical agents, adjuvants, and the like.In some embodiments, the compounds of Formula I or Formula II, orpharmaceutically acceptable salts thereof, are co-administered with oneor more other myasthenia gravis therapeutic agents, including, forexample, anticholinesterase agents (e.g., neostigmine, pyridostigmine,ambenonium chloride), immunosuppressive agents (e.g., prednisone,cyclosporine, azathioprine, mycophenolate mofetil) and intravenousimmune globulin. In other embodiments, the compounds of Formula I orFormula II, or pharmaceutically acceptable salts thereof, areadministered in combination with one or more procedures used to treatmyasthenia gravis, including, for example, thymectomy andplasmapheresis.

When the chemical entities disclosed herein are administered incombination with other therapeutic agents or procedures, the doses ofone or both agents will in some instances be lower than thecorresponding dose for single-agent therapy. Also, in general, thechemical entities described herein and the other therapeutic agent(s) donot have to be administered in the same pharmaceutical composition, andmay, because of different physical and chemical characteristics, beadministered by different routes. For example, one compound can beadministered orally, while the other is administered intravenously.Alternatively, each agent may be administerd by the same route. Thedetermination of the mode of administration and the advisability ofadministration, where possible, in the same pharmaceutical composition,is well within the knowledge of the skilled clinician. The initialadministration can be made according to established protocols known inthe art, and then, based upon the observed effects, the dosage, modes ofadministration and times of administration can be modified by theskilled clinician.

The chemical entities disclosed herein and the other therapeuticagent(s) and/or procedure(s) may be administered concurrently (e.g.,simultaneously, essentially simultaneously or within the same treatmentprotocol) sequentially (i.e., one followed by the other, with anoptional time interval in between), or a combination of simultaneouslyand sequentially (i.e., simultaneous administration of both agentsfollowed by administration of one agent, or administration of one agentfollowed by simultaneous administration of both agents) depending uponthe condition of the patient and the choice of other therapeuticagent(s) and/or procedure(s).

If the chemical entities disclosed herein and the other therapeuticagent(s) and/or procedure(s) are not administered simultaneously oressentially simultaneously, then the optimum order of administration maybe different for different patients. Thus, in certain situations thecompound(s) of Formula I or Formula II may be administered firstfollowed by the administration of the other therapeutic agent(s) and/orprocedure(s); and in other situations the other therapeutic agent(s)and/or procedure(s) may be administered first followed by theadministration of compound(s) of Formula I or Formula II. This alternateadministration may be repeated during a single treatment protocol. Forexample, the other therapeutic agent(s) and/or procedure(s) may beadministered first and then the treatment continued with theadministration of compound(s) of Formula I or Formula II followed, wheredetermined advantageous, by the administration of the other therapeuticagent(s) and/or procedure(s), and so on until the treatment protocol iscomplete. The determination of the order of administration, and thenumber of repetitions of administration of each therapeutic agent duringa treatment protocol, is well within the knowledge of the skilledphysician after evaluation of the disease being treated and thecondition of the patient.

Additional suitable medicinal and pharmaceutical agents includemodulators of one or more of skeletal myosin, skeletal actin, skeletaltropomyosin, skeletal troponin C, skeletal troponin I, skeletal troponinT, and skeletal muscle, including fragments and isoforms thereof, andthe skeletal sarcomere and other suitable therapeutic agents useful inthe treatment of the aforementioned disorders including: anti-obesityagents, anti-sarcopenia agents, anti-wasting syndrome agents,anti-frailty agents, anti-cachexia agents, anti-muscle spasm agents,agents against post-surgical and post-traumatic muscle weakness, andanti-neuromuscular disease agents, as well as the agents described inU.S. Patent Application No. 2005/0197367.

Suitable additional medicinal and pharmaceutical agents include, forexample: orlistat, sibramine, diethylpropion, phentermine,benzaphetamine, phendimetrazine, estrogen, estradiol, levonorgestrel,norethindrone acetate, estradiol valerate, ethinyl estradiol,norgestimate, conjugated estrogens, esterified estrogens,medroxyprogesterone acetate, testosterone, insulin-derived growthfactor, human growth hormone, riluzole, cannabidiol, prednisone,albuterol, non-steroidal anti-inflammatory drugs, and botulinum toxin.

Other suitable medicinal and pharmaceutical agents include TRH,diethylstilbesterol, theophylline, enkephalins, E series prostaglandins,compounds disclosed in U.S. Pat. No. 3,239,345 (e.g., zeranol),compounds disclosed in U.S. Pat. No. 4,036,979 (e.g., sulbenox),peptides disclosed in U.S. Pat. No. 4,411,890 growth hormonesecretagogues such as GHRP-6, GHRP-1 (disclosed in U.S. Pat. No.4,411,890 and publications WO 89/07110 and WO 89/07111), GHRP-2(disclosed in WO 93/04081), NN703 (Novo Nordisk), LY444711 (Lilly),MK-677 (Merck), CP424391 (Pfizer) and B-HT920, growth hormone releasingfactor and its analogs, growth hormone and its analogs and somatomedinsincluding IGF-1 and IGF-2, alpha-adrenergic agonists, such as clonidineor serotonin 5-HT_(D) agonists, such as sumatriptan, agents whichinhibit somatostatin or its release, such as physostigmine,pyridostigmine, parathyroid hormone, PTH(1-34), and bisphosphonates,such as MK-217 (alendronate).

Still other suitable medicinal and pharmaceutical agents includeestrogen, testosterone, selective estrogen receptor modulators, such astamoxifen or raloxifene, other androgen receptor modulators, such asthose disclosed in Edwards, J. P. et. al., Bio. Med. Chem. Let., 9,1003-1008 (1999) and Hamann, L. G. et. al., J. Med. Chem., 42, 210-212(1999), and progesterone receptor agonists (“PRA”), such aslevonorgestrel, medroxyprogesterone acetate (MPA).

Still other suitable medicinal and pharmaceutical agents include aP2inhibitors, such as those disclosed in U.S. Ser. No. 09/519,079 filedMar. 6, 2000, PPAR gamma antagonists, PPAR delta agonists, beta 3adrenergic agonists, such as AJ9677 (Takeda/Dainippon), L750355 (Merck),or CP331648 (Pfizer), other beta 3 agonists as disclosed in U.S. Pat.Nos. 5,541,204, 5,770,615, 5,491,134, 5,776,983 and 5,488,064, a lipaseinhibitor, such as orlistat or ATL-962 (Alizyme), a serotonin (anddopamine) reuptake inhibitor, such as sibutramine, topiramate (Johnson &Johnson) or axokine (Regeneron), a thyroid receptor beta drug, such as athyroid receptor ligand as disclosed in WO 97/21993, WO 99/00353, andGB98/284425, and anorectic agents, such as dexamphetamine, phentermine,phenylpropanolamine or mazindol.

Still other suitable medicinal and pharmaceutical agents include HIV andAIDS therapies, such as indinavir sulfate, saquinavir, saquinavirmesylate, ritonavir, lamivudine, zidovudine, lamivudine/zidovudinecombinations, zalcitabine, didanosine, stavudine, and megestrol acetate.

Still other suitable medicinal and pharmaceutical agents includeantiresorptive agents, hormone replacement therapies, vitamin Danalogues, elemental calcium and calcium supplements, cathepsin Kinhibitors, MMP inhibitors, vitronectin receptor antagonists, SrcSH.sub.2 antagonists, vacular —H⁺-ATPase inhibitors, ipriflavone,fluoride, Tibo lone, pro stanoids, 17-beta hydroxysteroid dehydrogenaseinhibitors and Src kinase inhibitors.

The above other therapeutic agents, when employed in combination withthe chemical entities described herein, may be used, for example, inthose amounts indicated in the Physicians' Desk Reference (PDR) or asotherwise determined by one of ordinary skill in the art.

In certain embodiments, the compositions will take the form of a pill ortablet and thus the composition will contain, along with the activeingredient, a diluent such as lactose, sucrose, dicalcium phosphate, orthe like; a lubricant such as magnesium stearate or the like; and abinder such as starch, gum acacia, polyvinylpyrrolidine, gelatin,cellulose, cellulose derivatives or the like. In another solid dosageform, a powder, marume, solution or suspension (e.g., in propylenecarbonate, vegetable oils or triglycerides) is encapsulated in a gelatincapsule.

Liquid pharmaceutically administrable compositions can, for example, beprepared by dissolving, dispersing, etc. at least one chemical entityand optional pharmaceutical adjuvants in a carrier (e.g., water, saline,aqueous dextrose, glycerol, glycols, ethanol or the like) to form asolution or suspension. Injectables can be prepared in conventionalforms, either as liquid solutions or suspensions, as emulsions, or insolid forms suitable for dissolution or suspension in liquid prior toinjection. The percentage of chemical entities contained in suchparenteral compositions is highly dependent on the specific naturethereof, as well as the activity of the chemical entities and the needsof the subject. However, percentages of active ingredient of 0.01% to10% in solution are employable, and will be higher if the composition isa solid which will be subsequently diluted to the above percentages. Incertain embodiments, the composition will comprise from about 0.2 to 2%of the active agent in solution.

Pharmaceutical compositions of the chemical entities described hereinmay also be administered to the respiratory tract as an aerosol orsolution for a nebulizer, or as a microfine powder for insufflation,alone or in combination with an inert carrier such as lactose. In such acase, the particles of the pharmaceutical composition have diameters ofless than 50 microns, in certain embodiments, less than 10 microns.

The following examples serve to more fully describe the manner of usingthe above-described invention. It is understood that these examples inno way serve to limit the true scope of this invention, but rather arepresented for illustrative purposes.

Example 1 Synthesis of(S)-6-bromo-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol

Step 1: (S)-6-bromo-N²-(1-phenylethyl)pyrazine-2,3-diamine. Athick-walled microwave bottle equipped with a stirbar was charged with1.0 equiv of 3,5-dibromopyrazin-2-amine and 6.6 equiv of(S)-sec-phenethylamine. The bottle was fitted with a septum and cap andheated to 180° C. in a microwave for 30 min. The resulting solution wasadsorbed onto 20 g of silica; flash chromatography (10%-50%EtOAc/Hexanes) provided the title compound (60%) as an off-white foam.LCMS m/z (APCI)=293.0, 295.0 (M+H).

Step 2: (S)-6-bromo-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol. Toa solution of (S)-6-bromo-N²-(1-phenylethyl)pyrazine-2,3-diamine (1.0equiv) in refluxing anhydrous THF (5 volume equivalents) was addedcarbonyldiimidazole (CDI). Successive portions of CDI were added untilthe starting material was consumed (approx. 3.6 equiv total) as judgedby TLC (50% EtOAc/Hexanes). After complete reaction, the mixture wascooled to room temperature and quenched by the careful addition of wateruntil gas evolution had ceased. The mixture was diluted with 25 volumeequivalents of EtOAc and washed with 3×7.5 volume equivalents of waterand 1×7.5 volume equivalents of brine. The organic layer was dried overanhydrous sodium sulfate, filtered and concentrated in vacuo. Flashchromatography (Biotage MPLC 5%-40% EtOAc/Hexanes) provided the titlecompound (66%) as a white solid. LCMS m/z (APCI)=319.0, 321.0 (M+H).

Example 1(a)

(S)-1-(2-hydroxy-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-6-yl)ethanone.An oven-dried scintillation vial equipped with a stirbar was chargedwith (S)-6-bromo-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol (1.0equiv), and (Ph₃P)₄Pd (0.07 equiv). The bottle was covered with a sheetof Parafilm and purged with nitrogen for 5 min, and anhydous dioxane (13volume equivalents), triethylamine (3.0 equiv), andtributyl(1-ethoxyvinyl)stannane (1.5 equiv) were added by syringe. Theresulting mixture was heated to 80° C. overnight. The reaction wasquenched with 1N KHSO₄ and stirred for 30 min. The mixture was thendiluted with EtOAc, washed twice with NaHCO₃ and once with brine. Theorganic layer was dried over sodium sulfate, filtered, and concentratedin vacuo. Flash chromatography (Biotage MPLC 10%-66% EtOAc/Hexanes)provided the title compound (33%) as a white solid. LCMS m/z(APCI)=283.1 (M+H).

Example 1(b)

(S,E)-1-(1-phenylethyl)-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2-ol. Athick-walled microwave bottle equipped with a stirbar was charged with(S)-6-bromo-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol (1.0 equiv),and (Ph₃P)₄Pd (0.12 equiv). The bottle was covered with a sheet ofParafilm and purged with nitrogen for 5 min, and N-methylpyrrolidone (14volume equivalents), triethyl amine (2.0 equiv), and(E)-tributyl(prop-1-enyl)stannane (3.0 equiv) were added by syringe. Theresulting mixture was immediately fitted with a septum and cap andheated to 120° C. in a microwave for 20 min. The reaction was thendiluted with EtOAc, washed four times with saturated aq. NaHCO₃ and oncewith brine. The organic layer was dried over sodium sulfate, filtered,and concentrated in vacuo. Reverse-phase preparative HPLC provided thetitle compound (54%) as a foam. LCMS m/z (APCI)=281.1 (M+H).

Example 1(c)

(S)-6-(methylthio)-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol. Athick-walled microwave bottle equipped with a stirbar was charged with(S)-6-bromo-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol (1.0 equiv),sodium thiomethoxide (4.5 equiv), and N-methylpyrrolidone (10 volumeequivalents). The bottle was fitted with a septum and cap and heated to180° C. in a microwave for 30 min. The reaction mixture was then dilutedwith 100 volume equivalents of EtOAc and washed with 4×100 volumeequivalents of water and 1×100 volume equivalents of brine. The organiclayer was dried over anhydrous sodium sulfate, filtered, andconcentrated in vacuo. Reverse-phase preparative HPLC (20%-80% MeCN/H₂O)provided the title compound (24%) as a white solid. LCMS m/z(APCI)=287.1 (M+H).

Example 1(d)

(S,Z)-1-(1-phenylethyl)-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2-ol. Ascintillation vial equipped with a stirbar was charged with(S)-6-bromo-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol (1.0 equiv),(Z)-prop-1-enyl boronic acid (2.0 equiv) and (DPPF)PdCl₂ (0.10 equiv).The vial was fitted with a septum-lined cap and purged with nitrogen for5-10 min. To this mixture was added dioxane (16.6 volume equivalents)and degassed 2N K₂CO₃ (4.2 volume equivalents) by syringe. The resultingmixture was heated to 90° C. overnight. The mixture was cooled to roomtemperature, diluted with EtOAc, washed with twice with saturated aq.NaHCO3, and once with brine. The organic layer was dried over sodiumsulfate, filtered, and concentrated in vacuo. Flash chromatography(Biotage MPLC 5%-40% EtOAc/Hexanes) provided the title compound (63%) asan off-white foam. LCMS m/z (APCI)=281.1 (M+H).

Example 1(e)

(S)-1-(1-phenylethyl)-6-vinyl-1H-imidazo[4,5-b]pyrazin-2-ol. Ascintillation vial equipped with a stirbar was charged with(S)-6-bromo-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol (1.0 equiv),vinyl boronic acid (2.2 equiv), and (DPPF)PdCl₂ (0.10 equiv). The vialwas fitted with a septum-lined cap and purged with nitrogen for 5-10min. To this mixture was added dioxane (16.6 volume equivalents) anddegassed 2N K₂CO₃ (4.2 volume equivalents) by syringe. The resultingmixture was heated to 90° C. overnight. The mixture was cooled to roomtemperature, diluted with 12 volume equivalents EtOAc, washed with twicewith saturated aq. NaHCO₃, and once with brine. The organic layer wasdried over sodium sulfate, filtered, and concentrated in vacuo. Flashchromatography (Biotage MPLC 5%-40% EtOAc/Hexanes) provided the titlecompound as an off-white solid (54%). LCMS m/z (APCI)=267.0 (M+H).

Example 1(f)

(S)-6-methoxy-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol. Athick-walled microwave bottle equipped with a stirbar was charged withMeOH (2.0 equiv) and NMP (20 volume equivalents). To the resultingsolution was added NaH (2.0 equiv), resulting in gas evolution.(S)-6-Bromo-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol (1.0 equiv)was then added to the reaction, and the resulting mixture wasimmediately fitted with a septum and cap and heated to 200° C. in amicrowave for 30 min. The reaction was then diluted with EtOAc, washedtwice with saturated aq. NaHCO₃ and once with brine. The organic layerwas dried over sodium sulfate, filtered, and concentrated in vacuo.Reverse-phase preparative HPLC provided the title compound (29%) as awhite solid. LCMS m/z (APCI)=271.1 (M+H).

Example 1(g)

(S)-1-(1-phenylethyl)-6-ethyl-1H-imidazo[4,5-b]pyrazin-2-ol. Ascintillation vial equipped with a stirbar was charged with(S)-6-vinyl-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol (1.0 equiv),methanol (280 volume equivalents), and catalytic Pd/C. The resultingmixture was purged with hydrogen for 45 minutes; the reaction wascomplete as judged my LCMS. The mixture was then filtered through a padof diatomaceous earth and the pad of diatomaceous earth was washed twicewith MeOH. The solution was concentrated in vacuo. Flash chromatography(Biotage MPLC 5%-40% EtOAc/Hexanes) provided the title compound (86%) asa foam. LCMS m/z (APCI)=269.1 (M+H).

Example 2 Synthesis of6-bromo-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2-ol

Step 1: 6-bromo-N²-(pentan-3-yl)pyrazine-2,3-diamine. The title compoundwas prepared in a manner analogous to Example 1 Step 1 except that3-aminopentane (2.6 volume equivalents) was substituted for(S)-sec-phenethylamine. LCMS m/z (APCI)=259.0, 260.0 (M+H).

Step 2: 6-bromo-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2-ol. The titlecompound was prepared by treating6-bromo-N²-(pentan-3-yl)pyrazine-2,3-diamine in a manner analogous toExample 1 Step 2 LCMS m/z (APCI)=285.0, 287.0 (M+H).

Example 2(a)

(E)-1-(pentan-3-yl)-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2-ol. Athick-walled microwave bottle equipped with a stirbar was charged with6-bromo-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2-ol (1.0 equiv) and(Ph₃P)₄Pd (0.15 equiv). The bottle was covered with a sheet of Parafilmand purged with nitrogen for 5-10 min, and N-methylpyrrolidone (11.7volume equivalents), triethyl amine (2.0 equiv), and(E)-tributyl(prop-1-enyl)stannane (2.0 equiv) were added by syringe. Theresulting mixture was immediately fitted with a septum and cap andheated to 120° C. in a microwave for 20 min. The reaction was thendiluted with EtOAc, washed with three times with water and once withbrine. The organic layer was dried over sodium sulfate, filtered, andconcentrated in vacuo. Reverse-phase preparative HPLC provided the titlecompound (15%) as a foam. LCMS m/z (APCI)=247.1 (M+H).

Example 2(b)

6-(methylthio)-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2-ol. The titlecompound was prepared by reacting6-bromo-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2-ol (1.0 equiv),sodium thiomethoxide (1.4 equiv), and N-methylpyrrolidone (5.9 volumeequivalents) in a manner analagous to Example 1(c). LCMS m/z(APCI)=253.0 (M+H).

Example 2(c)

(Z)-1-(pentan-3-yl)-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2-ol. Thetitle compound was prepared by reacting6-bromo-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2-ol (1.0 equiv),(Z)-prop-1-enyl boronic acid (1.5 equiv) and (DPPF)PdCl₂ (0.15 equiv) ina manner analagous to Example 1(d). LCMS m/z (APCI)=247.0 (M+H).

Example 3 Synthesis of 1-(pentan-3-yl)-1H-imidazo[4,5-b]quinoxalin-2-ol

Step 1: N²-(pentan-3-yl)quinoxaline-2,3-diamine. A thick-walledmicrowave bottle equipped with a stirbar was charged with3-chloroquinoxalin-2-amine (1.0 equiv) and 20 volume equivalents of3-aminopentane. The bottle was fitted with a septum and cap and heatedto 120° C. in a microwave for 30 min. The resulting solution wasconcentrated in vacuo. Flash chromatography (20%-60% EtOAc/Hexanes)provided the title compound (78%) as a yellow solid. LCMS m/z(APCI)=231.1 (M+H).

Step 2: 1-(pentan-3-yl)-1H-imidazo[4,5-b]quinoxalin-2-ol. The titlecompound was prepared by treatingN²-(pentan-3-yl)quinoxaline-2,3-diamine in a manner analogous to Example1 Step 2 LCMS m/z (APCI)=257.2 (M+H).

Example 3(a)

Synthesis of(Z)-1-(pentan-3-yl)-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2-ol. Ascintillation vial equipped with a stirbar was charged with6-bromo-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2-ol (1.0 equiv),KF₃BMe (2.0 equiv), Cs₂CO₃ (3.0 equiv) and (DPPF)PdCl₂ (0.20 equiv). Thevial was fitted with a septum-lined cap and purged with nitrogen for5-10 min. To this mixture was added dioxane (25 volume equivalents) anddegassed water (5 volume equivalents) by syringe. The resulting mixturewas heated to 90° C. overnight. The mixture was cooled to roomtemperature, diluted with 15 mL EtOAc, washed twice with saturated aq.NaHCO₃ and once with brine. The organic layer was dried over sodiumsulfate, filtered, and concentrated in vacuo. Flash chromatography(Biotage MPLC 5%-40% EtOAc/Hexanes) provided the title compound (53%) asa white solid. LCMS m/z (APCI)=221.1 (M+H).

Example 4 Synthesis of6-ethynyl-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2-ol Example 4(a)

1-(pentan-3-yl)-6-((trimethylsilyl)ethynyl)-1H-imidazo[4,5-b]pyrazin-2-ol.A mixture of 6-bromo-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2-ol (3.75g, 13.2 mmol)), trimethylsilylacetylene (2.8 mL, 19.8 mmol), PdCl₂(PPh)₂(0.93 g, 1.32 mmol), CuI (0.5 g, 2.64 mmol) and triethylamine (5.5 mL,39.5 mmol) in DMF (50 mL) was purged with N₂ for 30 seconds followed bystirring at 80° C. After 3 hours the reaction mixture was diluted withEtOAc, washed with NH₄Cl solution, dried over Na₂SO₄, and concentratedin vacuo. Purification with over silica gel (Biotage MPLC 10-80%EtOAc/hexanes) provided the title compound (3.2 g, 80%) as a brownsolid.

Example 4(b)

6-ethynyl-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2-ol. A mixture of1-(pentan-3-yl)-6-((trimethylsilyl)ethynyl)-1H-imidazo[4,5-b]pyrazin-2-ol(3.2 g, 10.6 mmol), KF (1.6 g, 27.5 mmol) in MeOH/THF/H₂O (50 mL, 2/2/1)was stirred at room temperature. Upon complete conversion by LCMS, thesolution was concentrated in vacuo, diluted with EtOAc, washed withNH₄Cl solution, dried over Na₂SO₄, and concentrated in vacuo.Purification over silica gel (Biotage MPLC 10-80% EtOAc/Heaxanes) gave abrown solid, which was washed with 15% EtOAc/hexanes to give product thetitle compound as a white solid (0.9 g, 37%).

Example 5 Synthesis of6-(dimethylamino)-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2-ol Example5(a)

tert-butyl5-bromo-2-oxo-3-(pentan-3-yl)-2,3-dihydroimidazo[4,5-b]pyrazine-1-carboxylate.To a solution of 6-bromo-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2-ol(5.0 g, 17.6 mmol) in DCM (80 mL) containing triethylamine (7.34 mL,52.8 mmol) was added Boc₂O (7.0 g, 35 mmol). The reaction mixture wasstirred at room temperature overnight, washed with NaHCO₃ solution,dried over Na₂SO₄ and concentrated in vacuo. Purification over silicagel (Biotage MPLC 10-50% EtOAc/hexanes) gave the desired product as awhite solid (1.7 g, 25%).

Example 5(b)

6-(dimethylamino)-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2-ol. Amixture of tert-butyl5-bromo-2-oxo-3-(pentan-3-yl)-2,3-dihydroimidazo[4,5-b]pyrazine-1-carboxylate(200 mg, 0.52 mmol), dimethylamine (0.5 mL, 2M in THF, 1.0 mmol),Pd₃(dba)₂ (48 mg, 0.052 mmol), BiPhP(Cy)₂ (37 mg, 0.10 mmol) and NaOtBu(150 mg, 1.56 mmol) in anhydrous toluene (4 mL) was purged with N₂ for15 second and then stirred at 120° C. for 20 minutes in microwave. Themixture was diluted with EtOAc, washed with NaHCO₃ solution, dried overNa₂SO₄, and then concentrated in vacuo to give a dark muddy residue. Theresidue was dissolved in MeOH (10 mL) and treated with 1 mL 4M HCl indioxane. After one hour, the reaction was concentrated, diluted withEtOAc, washed with NaHCO₃, dried over Na₂SO₄, and concentrated in vacuo.Purification over silica gel (Biotage MPLC 10-70% EtOAc/hexanes) gavethe title compound as a light yellow solid (42 mg, 32%).

Example 6 Preparation of Sarcomeric Proteins from Skeletal Muscle

Actin was purified by first preparing an ether powder of cardiac muscle(Zot H G and Potter J D. (1981) Preparative Biochemistry 11:381-395) asdescribed below. Subsequently, actin was cycled between the filamentousand soluble state through rounds of centrifugation and dialysis (SpudichJ A and Watt S. (1971) J. Biol. Chem. 246:4866-4871). It was stored inthe filamentous state at 4° C.

Tropomyosin was extracted from the ether powder and separated from theother proteins based on pH dependent precipitations followed bysuccessive ammonium sulfate cuts at 53% and 65% (Smillie L B. (1981)Methods Enzymol 85 Pt B:234-41). The troponins were isolated as anintact complex of TnC, TnT, and TnI. Ether powder is extracted in a highsalt buffer. Successive ammonium sulfate cuts of 30% and 45% were done;the precipitate was solubilized by dialysis into a low salt buffer andthen further purified on a DEAE Toyopearl column with a 25-350 mM KClgradient. There was no measurable ATPase in any of the components exceptfor myosin which naturally had a very low basal ATPase in the absence ofactin.

Just prior to screening, the actin, tropomyosin, and troponin complexare mixed together in the desired ratio (e.g., 7:1:1) to achieve maximalcalcium regulation of the actin filament. The screen is conducted at apCa=6.5. This calcium concentration is in the physiological range duringmuscle contraction.

To measure the generation of ADP during the reaction, a pyruvatekinase/lactate dehydrogenase/NADH coupled enzyme system (PK/LDH) isadded to the actin. The myosin is kept separately. The plates are readin real time so that kinetic curves are obtained. These compounds are inDMSO and were already spotted onto the bottoms of 384 well plates at 10to 40 μg/ml final concentration.

Example 7 Actin Preparation

-   -   1. Extract powder (as prepared in Example 8 or 9 below) with 20        ml buffer A (see below, add BME and ATP just prior to use in        each of the following steps) per gram of powder (200 ml per 10        g). Use a large 4 L beaker for 150 g of powder. Mix vigorously        to dissolve powder. Stir at 4° C. for 30 min.    -   2. Separate extract from the hydrated powder by squeezing        through several layers of cheesecloth. Cheesecloth should be        pre-sterilized by microwaving damp for 1-2 min.    -   3. Re-extract the residue with the same volume of buffer A and        combine extracts.    -   4. Spin in JLA10 rotor(s) for 1 hr at 10K rpm (4° C.). Collect        supernatant through 2 layers of cheesecloth.    -   5. Add ATP to 0.2 mM and MgCl₂ to 50 mM. Stir on stir plate at        4° C. for 60 minutes to allow actin to polymerize/form        para-crystals.    -   6. Slowly add solid KCl to 0.6 M (45 g/l). Stir at 4° C. for 30        min.    -   7. Spin in JLA10 rotor(s) at 10K rpm for 1 hr.    -   8. Depolymerization: Quickly rinse surface of pellets with        buffer A and dispose of wash. Soften the pellets by        pre-incubation on ice with small amount of buffer A in each tube        (use less than half of final resuspension volume total in all        tubes). Resuspend by hand first with cell scraper and combine        pellets. Wash tubes with extra buffer using a 25 ml pipette and        motorized pipettor, aggressively removing actin from sides of        tubes. Homogenize in large dounce in cold buffer A on ice. Use 3        ml per gram of powder originally extracted.    -   9. Dialyze against buffer A with 4 changes over 48 hour period.    -   10. Collect dialyzed actin and spin in the 45Ti rotor at 40K rpm        for 1.5 hr (4° C.).    -   11. Collect supernatant (G-Actin). Save a sample for gel        analysis and determination of protein concentration.

To polymerize G-actin for storage add KCl to 50 mM (from 3 M stock),MgCl₂ to 1 mM, and NaN₃ to 0.02% (from 10% stock). Store at 4° C. Do notfreeze.

Buffer A: 2 mM tris/HCl, 0.2 mM CaCl₂, 0.5 mM (36 μl/L)2-mercaptoethanol, 0.2 mM Na₂ ATP (added fresh), and 0.005% Na-azide; pH8.0.

Example 8 Powder Preparation

-   -   1. Volumes are given per about 1000 g of the minced muscle.    -   2. Pre-cut and boil cheesecloth for 10 min in water. Drain and        dry.    -   3. Mince chicken breast in a prechilled meat grinder.    -   4. Extract with stirring in 2 L of 0.1 M KCl, 0.15 M        K-phosphate, pH 6.5 for 10 min at 4° C. Spin 5000 rpm, 10 min,        4° C. in JLA. Collect the pellet.    -   5. Extract pellets with stirring with 2 L of 0.05 M NaHCO₃ for 5        min. Spin 5000 rpm, 10 min, 4° C. in JLA. Collect the pellet.        Repeat the extraction once more.    -   6. Extract the filtered residue with 2 L of 1 mM EDTA, pH 7.0        for 10 min with stirring.    -   7. Extract with 2 L of H₂O for 5 min with stirring. Spin 10000        rpm, 15 min, 4° C. in JLA. Carefully collect the pellet, part of        which will be loose and gelatinous.    -   8. Extract 5 times with acetone (2 L of acetone for 10 min each        with stirring). Squeeze through cheesecloth gently. All acetone        extractions are performed at room temperature. Acetone should be        prechilled to 4° C.    -   9. Drying: Place the filtered residue spread on a cheesecloth in        a large glass tray and leave in a hood overnight. When the        residue is dry, put in a wide mouth plastic bottle and store at        20° C.

Example 9 Alternate Powder Preparation

Based on Zot & Potter (1981) Prep. Biochem. 11(4) pp.381-395.

-   -   1. Dissect left ventricles of the cardiac muscle. Remove as much        of the pericardial tissue and fat as possible. Grind in a        prechilled meat grinder. Weigh.    -   2. Prepare 5 volumes of Extract buffer (see below). Be sure the        pH=8.0. Then, homogenize the meat in a blender, 4 times 15 sec        on blend with 15 secs in between. Do this with 1 volume        weight/volume) of buffer taken from the 5 volumes already        prepared. Add the homogenate back to the extract buffer and stir        until well mixed (5 minutes).    -   3. Filter through one layer of cheesecloth in large        polypropylene strainer. Resuspend back into 5 volumes of extract        buffer as above.    -   4. Repeat Step 3 four more times. At the end, do not resuspend        in extraction buffer but proceed to Step 5. The pellets should        be yellow white.    -   5. Resuspend in 3 volumes (according to original weight) of 95%        cold ethanol. Stir for 5 min and squeeze through cheesecloth as        above, repeat two more times.    -   6. Weigh squeezed residue and then resuspend in 3 volumes (new        weight/volume) of cold diethyl ether.    -   7. Repeat Step 6 a total of three times.    -   8. Leave overnight in a single layer on a cheesecloth in a glass        tray.    -   9. When dry, collect the powder, weigh and store in a wide-mouth        jar at 4° C.        EXTRACT BUFFER: 50 mM KCl, 5 mM Tris pH 8.0

Prepare as 50 times concentrate:

For 2 L

250 mM Tris pH 8.0. Tris Base (121.14 g/mol, 60.6 g)

pH to 8.0 with conc. HCl, then add:

2.5 M KCl (74.55 g/mol, 372 g)

Example 10 Purification of Skeletal Muscle Myosin

See, Margossian, S. S. and Lowey, S. (1982) Methods Enzymol. 85, 55-123and Goldmann, W. H. and Geeves, M. A. (1991) Anal. Biochem. 192, 55-58.

-   Solution A: 0.3 M KCl, 0.15 M potassium phosphate, 0.02 M EDTA,    0.005 M MgCl₂, 0.001 M ATP, pH 6.5.-   Solution B: 1 M KCl, 0.025 M EDTA, 0.06 M potassium phosphate, pH    6.5.-   Solution C: 0.6 M KCl, 0.025 M potassium phosphate, pH 6.5.-   Solution D: 0.6 M KCl, 0.05 M potassium phosphate, pH 6.5.-   Solution E: 0.15 M potassium phosphate, 0.01 M EDTA, pH 7.5.-   Solution F: 0.04 M KCl, 0.01 M potassium phosphate, 0.001 M DTT, pH    6.5.-   Solution G: 3 M KCl, 0.01 M potassium phosphate, pH 6.5.    All procedures are carried out at 4° C.    -   1. Obtain ˜1000 g skeletal muscle, such as rabbit skeletal        muscle.    -   2. Grind twice; extract with 2 L solution A for 15 min while        stirring; add 4 L cold H₂O, filter through gauze; dilute with        cold H₂O to ionic strength of 0.04, (about 10-fold); let settle        for 3 h; collect precipitate at 7,000 rpm in GSA rotor for 15        min.    -   3. Disperse pellet in 220 ml solution B; dialyze overnight        against 6 L solution C; slowly add ˜400 ml equal volume cold        distilled H₂O; stir for 30 min; centrifuge at 10,000 rpm for 10        min in GSA rotor.    -   4. Centrifuge supernatant at 19,000 rpm for 1 h.    -   5. Dilute supernatant to ionic strength of 0.04 (˜8-fold); let        myosin settle overnight; collect about 5-6 L fluffy myosin        precipitate by centrifuging at 10,000 rpm for 10 min in GSA        rotor.    -   6. Resuspend pellet in minimal volume of solution G; dialyze        overnight against 2 L solution D; centrifuge at 19,000 rpm for 2        h, in cellulose nitrate tubes; puncture tubes and separate        myosin from fat and insoluble pellet.    -   7. Dilute supernatant to 5-10 mg/ml and dialyze against solution        E extensively, load onto DEAE-sephadex column.    -   8. Preequilibrate with solution E; apply 500-600 g myosin at 30        ml/h; wash with 350 ml solution E; elute with linear gradient of        0-0.5 M KCl in solution E (2×1 liter); collect 10 ml fractions;        pool myosin fractions (>0.1 M KCl); concentrate by overnight        dialysis against solution F; centrifuge at 25,000 rpm for 30        min; store as above.    -   9. The myosin is then cut with chymotrypsin or papain in the        presence of EDTA to generate the 51 fragment which is soluble at        the low salt conditions optimal for ATPase activity (Margossian        supra).

Example 11

Using procedures similar to those described herein, the compounds in thefollowing table were synthesized and tested.

SKM MF AC1.4 Name m/z Ion (μM)(S)-6-bromo-1-(1-phenylethyl)-1H-imidazo[4,5- 319.0; [M + H]⁺; 0.45b]pyrazin-2-ol 321.0 [M + H]⁺(S)-6-bromo-1-(1-phenylethyl)-1H-imidazo[4,5- 319.0; [M + H]⁺; 0.45b]pyrazin-2(3H)-one 321.0 [M + H]⁺(R)-6-bromo-1-(1-phenylethyl)-1H-imidazo[4,5- 319.0; [M + H]⁺; 2.4b]pyrazin-2-ol 321.0 [M + H]⁺(R)-6-bromo-1-(1-phenylethyl)-1H-imidazo[4,5- 319.0; [M + H]⁺; 2.4b]pyrazin-2(3H)-one 321.0 [M + H]⁺1-benzyl-6-bromo-1H-imidazo[4,5-b]pyrazin-2-ol 305.1; [M + H]⁺; 23.5307.1 [M + H]⁺ 1-benzyl-6-bromo-1H-imidazo[4,5-b]pyrazin- 305.1; [M +H]⁺; 23.5 2(3H)-one 307.1 [M + H]⁺(S)-6-(methylthio)-1-(1-phenylethyl)-1H- 287.1 [M + H]⁺ 1.1imidazo[4,5-b]pyrazin-2-ol (S)-6-(methylthio)-1-(1-phenylethyl)-1H-287.1 [M + H]⁺ 1.1 imidazo[4,5-b]pyrazin-2(3H)-one1-benzyl-6-(methylthio)-1H-imidazo[4,5-b]pyrazin- 273.0 [M + H]⁺ 22.62-ol 1-benzyl-6-(methylthio)-1H-imidazo[4,5-b]pyrazin- 273.0 [M + H]⁺22.6 2(3H)-one (R)-6-(methylthio)-1-(1-phenylethyl)-1H- 287.0 [M + H]⁺2.9 imidazo[4,5-b]pyrazin-2-ol (R)-6-(methylthio)-1-(1-phenylethyl)-1H-287.0 [M + H]⁺ 2.9 imidazo[4,5-b]pyrazin-2(3H)-one(S)-6-(2-methylprop-1-enyl)-1-(1-phenylethyl)-1H- 295.1 [M + H]⁺ 2.7imidazo[4,5-b]pyrazin-2-ol(S)-6-(2-methylprop-1-enyl)-1-(1-phenylethyl)-1H- 295.1 [M + H]⁺ 2.7imidazo[4,5-b]pyrazin-2(3H)-one (S)-6-cyclohexenyl-1-(1-phenylethyl)-1H-321.1 [M + H]⁺ 31.0 imidazo[4,5-b]pyrazin-2-ol(S)-6-cyclohexenyl-1-(1-phenylethyl)-1H- 321.1 [M + H]⁺ 31.0imidazo[4,5-b]pyrazin-2(3H)-one(S,Z)-1-(1-phenylethyl)-6-(prop-1-enyl)-1H- 281.1 [M + H]⁺ 1.0imidazo[4,5-b]pyrazin-2-ol (S,Z)-1-(1-phenylethyl)-6-(prop-1-enyl)-1H-281.1 [M + H]⁺ 1.0 imidazo[4,5-b]pyrazin-2(3H)-one(S)-1-(1-phenylethyl)-6-vinyl-1H-imidazo[4,5- 267.0 [M + H]⁺ 2.4b]pyrazin-2-ol (S)-1-(1-phenylethyl)-6-vinyl-1H-imidazo[4,5- 267.0 [M +H]⁺ 2.4 b]pyrazin-2(3H)-one(S)-6-ethyl-1-(1-phenylethyl)-1H-imidazo[4,5- 269.1 [M + H]⁺ 17.4b]pyrazin-2-ol (S)-6-ethyl-1-(1-phenylethyl)-1H-imidazo[4,5- 269.1 [M +H]⁺ 17.4 b]pyrazin-2(3H)-one(S)-1-(1-phenylethyl)-6-propyl-1H-imidazo[4,5- 283.1 [M + H]⁺ 29.7b]pyrazin-2-ol (S)-1-(1-phenylethyl)-6-propyl-1H-imidazo[4,5- 283.1 [M +H]⁺ 29.7 b]pyrazin-2(3H)-one(S)-6-methoxy-1-(1-phenylethyl)-1H-imidazo[4,5- 271.1 [M + H]⁺ 8.8b]pyrazin-2-ol (S)-6-methoxy-1-(1-phenylethyl)-1H-imidazo[4,5- 271.1[M + H]⁺ 8.8 b]pyrazin-2(3H)-one6-bromo-1-cyclohexyl-1H-imidazo[4,5-b]pyrazin-2- 296.9; [M + H]⁺; 10.4ol 298.9 [M + H]⁺ 6-bromo-1-cyclohexyl-1H-imidazo[4,5-b]pyrazin- 296.9;[M + H]⁺; 10.4 2(3H)-one 298.9 [M + H]⁺1-cyclohexyl-6-(methylthio)-1H-imidazo[4,5- 265.1 [M + H]⁺ 13.9b]pyrazin-2-ol 1-cyclohexyl-6-(methylthio)-1H-imidazo[4,5- 265.1 [M +H]⁺ 13.9 b]pyrazin-2(3H)-one(Z)-1-cyclohexyl-6-(prop-1-enyl)-1H-imidazo[4,5- 259.1 [M + H]⁺ 6.0b]pyrazin-2-ol (Z)-1-cyclohexyl-6-(prop-1-enyl)-1H-imidazo[4,5- 259.1[M + H]⁺ 6.0 b]pyrazin-2(3H)-one(E)-1-cyclohexyl-6-(prop-1-enyl)-1H-imidazo[4,5- 259.1 [M + H]⁺ 6.1b]pyrazin-2-ol (E)-1-cyclohexyl-6-(prop-1-enyl)-1H-imidazo[4,5- 259.1[M + H]⁺ 6.1 b]pyrazin-2(3H)-one(S,E)-1-(1-phenylethyl)-6-(prop-1-enyl)-1H- 281.1 [M + H]⁺ 1.6imidazo[4,5-b]pyrazin-2-ol (S,E)-1-(1-phenylethyl)-6-(prop-1-enyl)-1H-281.1 [M + H]⁺ 1.6 imidazo[4,5-b]pyrazin-2(3H)-one6-bromo-1-isopropyl-1H-imidazo[4,5-b]pyrazin-2-ol 259.0 [M + H]⁺ 6.06-bromo-1-isopropyl-1H-imidazo[4,5-b]pyrazin- 259.0 [M + H]⁺ 6.02(3H)-one 1-isopropyl-6-(methylthio)-1H-imidazo[4,5- 225.1 [M + H]⁺ 6.7b]pyrazin-2-ol 1-isopropyl-6-(methylthio)-1H-imidazo[4,5- 225.1 [M + H]⁺6.7 b]pyrazin-2(3H)-one (Z)-1-isopropyl-6-(prop-1-enyl)-1H-imidazo[4,5-219.2 [M + H]⁺ 4.6 b]pyrazin-2-ol(Z)-1-isopropyl-6-(prop-1-enyl)-1H-imidazo[4,5- 219.2 [M + H]⁺ 4.6b]pyrazin-2(3H)-one (S)-6-ethoxy-1-(1-phenylethyl)-1H-imidazo[4,5- 285.2[M + H]⁺ 10.6 b]pyrazin-2-ol(S)-6-ethoxy-1-(1-phenylethyl)-1H-imidazo[4,5- 285.2 [M + H]⁺ 10.6b]pyrazin-2(3H)-one 6-bromo-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-286.0; [M + 2H]²⁺; 0.25 2-ol 288.0 [M + 2H]²⁺6-bromo-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin- 286.0; [M + 2H]²⁺;0.25 2(3H)-one 288.0 [M + 2H]²⁺6-(methylthio)-1-(pentan-3-yl)-1H-imidazo[4,5- 253.1 [M + H]⁺ 0.4b]pyrazin-2-ol 6-(methylthio)-1-(pentan-3-yl)-1H-imidazo[4,5- 253.1 [M +H]⁺ 0.4 b]pyrazin-2(3H)-one (E)-1-(pentan-3-yl)-6-(prop-1-enyl)-1H-247.1 [M + H]⁺ 0.4 imidazo[4,5-b]pyrazin-2-ol(E)-1-(pentan-3-yl)-6-(prop-1-enyl)-1H- 247.1 [M + H]⁺ 0.4imidazo[4,5-b]pyrazin-2(3H)-one (Z)-1-(pentan-3-yl)-6-(prop-1-enyl)-1H-247.1 [M + H]⁺ 0.6 imidazo[4,5-b]pyrazin-2-ol(Z)-1-(pentan-3-yl)-6-(prop-1-enyl)-1H- 247.1 [M + H]⁺ 0.6imidazo[4,5-b]pyrazin-2(3H)-one 6-methyl-1-(pentan-3-yl)-1H-imidazo[4,5-221.1 [M + H]⁺ 0.53 b]pyrazin-2-ol6-methyl-1-(pentan-3-yl)-1H-imidazo[4,5- 221.1 [M + H]⁺ 0.53b]pyrazin-2(3H)-one (S,Z)-6-(hex-2-enyl)-1-(1-phenylethyl)-1H- 3.1imidazo[4,5-b]pyrazin-2-ol 2-hydroxy-1-(pentan-3-yl)-1H-imidazo[4,5-232.1 [M + H]⁺ 36.4 b]pyrazine-6-carbonitrile2-oxo-3-(pentan-3-yl)-2,3-dihydro-1H-imidazo[4,5- 232.1 [M + H]⁺ 36.4b]pyrazine-5-carbonitrile (R)-6-bromo-1-sec-butyl-1H-imidazo[4,5- 273.0[M + H]⁺ 1.5 b]pyrazin-2-ol (R)-6-bromo-1-sec-butyl-1H-imidazo[4,5-273.0 [M + H]⁺ 1.5 b]pyrazin-2(3H)-one(S)-6-bromo-1-sec-butyl-1H-imidazo[4,5-b]pyrazin- 272.0 [M + 2H]²⁺ 0.82-ol (S)-6-bromo-1-sec-butyl-1H-imidazo[4,5-b]pyrazin- 272.0 [M + 2H]²⁺0.8 2(3H)-one 6-bromo-1-tert-butyl-1H-imidazo[4,5-b]pyrazin-2-ol 272.0[M + 2H]²⁺ 0.8 6-bromo-1-tert-butyl-1H-imidazo[4,5-b]pyrazin- 272.0 [M +2H]²⁺ 0.8 2(3H)-one 2-(6-bromo-2-hydroxy-1H-imidazo[4,5-b]pyrazin-1-299.0 [M − H]⁻ >49 yl)butanoic acid2-(6-bromo-2-oxo-2,3-dihydro-1H-imidazo[4,5- 299.0 [M − H]⁻ >49b]pyrazin-1-yl)butanoic acid2-(6-bromo-2-hydroxy-1H-imidazo[4,5-b]pyrazin-1- 370.0 [M + H]⁺ >49yl)-1-morpholinobutan-1-one 6-bromo-1-(1-morpholino-1-oxobutan-2-yl)-1H-370.0 [M + H]⁺ >49 imidazo[4,5-b]pyrazin-2(3H)-one(R)-6-bromo-1-(1-hydroxybutan-2-yl)-1H- 285.0 [M − H]⁻ 1.1imidazo[4,5-b]pyrazin-2-ol (R)-6-bromo-1-(1-hydroxybutan-2-yl)-1H- 285.0[M − H]⁻ 1.1 imidazo[4,5-b]pyrazin-2(3H)-one(S)-6-bromo-1-(1-hydroxybutan-2-yl)-1H- 285.0 [M − H]⁻ 19.1imidazo[4,5-b]pyrazin-2-ol (S)-6-bromo-1-(1-hydroxybutan-2-yl)-1H- 285.0[M − H]⁻ 19.1 imidazo[4,5-b]pyrazin-2(3H)-one6-bromo-1-(1-methoxybutan-2-yl)-1H-imidazo[4,5- 301.0 [M + H]⁺ 4.9b]pyrazin-2-ol 6-bromo-1-(1-methoxybutan-2-yl)-1H-imidazo[4,5- 301.0[M + H]⁺ 4.9 b]pyrazin-2(3H)-one1-(1-aminobutan-2-yl)-6-bromo-1H-imidazo[4,5- 287.0 [M + 2H]²⁺ 1.1b]pyrazin-2-ol 1-(1-aminobutan-2-yl)-6-bromo-1H-imidazo[4,5- 287.0 [M +2H]²⁺ 1.1 b]pyrazin-2(3H)-one 6-bromo-1-(1-(methylamino)butan-2-yl)-1H-300.0 [M + H]⁺ 45.7 imidazo[4,5-b]pyrazin-2-ol6-bromo-1-(1-(methylamino)butan-2-yl)-1H- 300.0 [M + H]⁺ 45.7imidazo[4,5-b]pyrazin-2(3H)-one6-bromo-1-(1-(dimethylamino)butan-2-yl)-1H- 315.0 [M + 2H]²⁺ 43.8imidazo[4,5-b]pyrazin-2-ol 6-bromo-1-(1-(dimethylamino)butan-2-yl)-1H-315.0 [M + 2H]²⁺ 43.8 imidazo[4,5-b]pyrazin-2(3H)-one6-bromo-1-(1-(4-methylpiperazin-1-yl)butan-2-yl)- 369.0 [M + H]⁺ 14.91H-imidazo[4,5-b]pyrazin-2-ol6-bromo-1-(1-(4-methylpiperazin-1-yl)butan-2-yl)- 369.0 [M + H]⁺ 14.91H-imidazo[4,5-b]pyrazin-2(3H)-one(R)-6-bromo-1-(1-morpholinobutan-2-yl)-1H- 356.0; [M + H]⁺; 0.3imidazo[4,5-b]pyrazin-2-ol 358.0 [M + H]⁺(R)-6-bromo-1-(1-morpholinobutan-2-yl)-1H- 356.0; [M + H]⁺; 0.3imidazo[4,5-b]pyrazin-2(3H)-one 358.0 [M + H]⁺(S)-6-bromo-1-(1-morpholinobutan-2-yl)-1H- 356.0; [M + H]⁺; >49imidazo[4,5-b]pyrazin-2-ol 358.0 [M + H]⁺(S)-6-bromo-1-(1-morpholinobutan-2-yl)-1H- 356.0; [M + H]⁺; >49imidazo[4,5-b]pyrazin-2(3H)-one 358.0 [M + H]⁺(E)-1-isopropyl-6-(prop-1-enyl)-1H-imidazo[4,5- 219.1 [M + H]⁺ 7.1b]pyrazin-2-ol (E)-1-isopropyl-6-(prop-1-enyl)-1H-imidazo[4,5- 219.1[M + H]⁺ 7.1 b]pyrazin-2(3H)-one1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2-ol 207.1 [M + H]⁺ 16.0^(†)1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)- 207.1 [M + H]⁺ 16.0^(†)one methyl 4-(2-(6-bromo-2-hydroxy-1H-imidazo[4,5- 414.0 [M + 2H]²⁺0.9^(†) b]pyrazin-1-yl)butyl)piperazine-1-carboxylate methyl4-(2-(6-bromo-2-oxo-2,3-dihydro-1H- 414.0 [M + 2H]²⁺ 0.9^(†)imidazo[4,5-b]pyrazin-1-yl)butyl)piperazine-1- carboxylate6-bromo-1-(1-(4-(methylsulfonyl)piperazin-1- 434.0 [M + 2H]²⁺ 3.2^(†)yl)butan-2-yl)-1H-imidazo[4,5-b]pyrazin-2-ol6-bromo-1-(1-(4-(methylsulfonyl)piperazin-1- 434.0 [M + 2H]²⁺ 3.2^(†)yl)butan-2-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one5-bromo-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin- 285.0; [M + H]⁺; 11.52-ol 287.0 [M + H]⁺ 5-bromo-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-285.0; [M + H]⁺; 11.5 2(3H)-one 287.0 [M + H]⁺1-(pentan-3-yl)-1H-imidazo[4,5-b]quinoxalin-2-ol 257.1 [M + H]⁺ 19.81-(pentan-3-yl)-1H-imidazo[4,5-b]quinoxalin- 257.1 [M + H]⁺ 19.82(3H)-one 6-ethynyl-1-(pentan-3-yl)-1H-imidazo[4,5- 231.2 [M + H]⁺0.1^(‡) b]pyrazin-2-ol 6-ethynyl-1-(pentan-3-yl)-1H-imidazo[4,5- 231.2[M + H]⁺ 0.1^(‡) b]pyrazin-2(3H)-one1-(pentan-3-yl)-6-(trifluoromethyl)-1H-imidazo[4,5- 275.2 [M + H]⁺10.4^(‡) b]pyrazin-2-ol1-(pentan-3-yl)-6-(trifluoromethyl)-1H-imidazo[4,5- 275.2 [M + H]⁺10.4^(‡) b]pyrazin-2(3H)-one6-bromo-1-(2-methyl-1-morpholinopropan-2-yl)- 356.0; [M + H]⁺; 16.4^(‡)1H-imidazo[4,5-b]pyrazin-2-ol 358.0 [M + H]⁺6-bromo-1-(2-methyl-1-morpholinopropan-2-yl)- 356.0; [M + H]⁺; 16.4^(‡)1H-imidazo[4,5-b]pyrazin-2(3H)-one 358.0 [M + H]⁺(S)-6-bromo-1-(1-morpholinopropan-2-yl)-1H- 342.0; [M + H]⁺; >49imidazo[4,5-b]pyrazin-2-ol 344.0 [M + H]⁺(S)-6-bromo-1-(1-morpholinopropan-2-yl)-1H- 342.0; [M + H]⁺; >49imidazo[4,5-b]pyrazin-2(3H)-one 344.0 [M + H]⁺6-methoxy-1-(pentan-3-yl)-1H-imidazo[4,5- 237.1 [M + H]⁺ 2.2^(‡)b]pyrazin-2-ol 6-methoxy-1-(pentan-3-yl)-1H-imidazo[4,5- 237.1 [M + H]⁺2.2^(‡) b]pyrazin-2(3H)-one (R)-6-bromo-1-(1-morpholinopropan-2-yl)-1H-342.0; [M + H]⁺; 5.2^(‡) imidazo[4,5-b]pyrazin-2-ol 344.0 [M + H]⁺(R)-6-bromo-1-(1-morpholinopropan-2-yl)-1H- 342.0; [M + H]⁺; 5.2^(‡)imidazo[4,5-b]pyrazin-2(3H)-one 344.0 [M + H]⁺1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazine-2,6-diol 223.2 [M + H]⁺ >496-hydroxy-1-(pentan-3-yl)-1H-imidazo[4,5- 223.2 [M + H]⁺ >49b]pyrazin-2(3H)-one 1-(pentan-3-yl)-6-(prop-1-ynyl)-1H-imidazo[4,5-245.2 [M + H]⁺ >49 b]pyrazin-2-ol1-(pentan-3-yl)-6-(prop-1-ynyl)-1H-imidazo[4,5- 245.2 [M + H]⁺ >49b]pyrazin-2(3H)-one 1-(1-morpholinobutan-2-yl)-1H-imidazo[4,5- 278.0[M + H]⁺ >49 b]pyrazin-2-ol 1-(1-morpholinobutan-2-yl)-1H-imidazo[4,5-278.0 >49 b]pyrazin-2(3H)-one 1-(ethylpropyl)-6-(1-methylpyrazol-4-287.1 [M + H]⁺ 15 yl)imidazo[4,5-b]pyrazin-2-ol6-bromo-1-(propylbutyl)imidazo[4,5-b]pyrazin-2-ol 313.1 [M + H]⁺ 0.71-[(1R)-3-methyl-1-(morpholin-4-ylmethyl)butyl]-6- 384 [M + H]⁺ 0.5bromoimidazo[4,5-b]pyrazin-2-ol1-(ethylpropyl)-6-vinylimidazo[4,5-b]pyrazin-2-ol 233.1 [M + H]⁺ 2.31-(ethylpropyl)-6-(1-methylvinyl)imidazo[4,5- 247 [M + H]⁺ 0.6b]pyrazin-2-ol 1-(ethylpropyl)-6-(methylethyl)imidazo[4,5- 249 [M + H]⁺29.6 b]pyrazin-2-ol 6-chloro-1-(ethylpropyl)imidazo[4,5-b]pyrazin-2-ol239.1 [M + H]⁺ 0.7 6-(dimethylamino)-1-(ethylpropyl)imidazo[4,5- 250.1[M + H]⁺ 2.2 b]pyrazin-2-ol 1-((1R)-1-methyl-2-morpholin-4-ylethyl)-6-342, (M + H), 5.19 bromoimidazo[4,5-b]pyrazin-2-ol 344 (M + 2 + H)1-(ethylpropyl)-6-ethynylimidazo[4,5-b]pyrazin-2-ol 229 (M − H) 0.151-(ethylpropyl)-6-methoxyimidazo[4,5-b]pyrazin-2- 237 (M − H) 2.20 ol1-(1,1-dimethyl-2-morpholin-4-ylethyl)-6- 356, (M + 1), 19.11bromoimidazo[4,5-b]pyrazin-2-ol 358 (M + 2 + H)6-(1H-1,2,3-triazol-4-yl)-1- 274 (M + H)+ 46.64(ethylpropyl)imidazo[4,5-b]pyrazin-2-ol1-(ethylpropyl)-6-(trifluoromethyl)imidazo[4,5- 275 (M + H) 10.37b]pyrazin-2-ol 1-[(1R)-1-(morpholin-4-ylmethyl)propyl]-6- 302 (M + H)0.13 ethynylimidazo[4,5-b]pyrazin-2-ol1-(ethylpropyl)-6-{2-[1-(ethylpropyl)-2- 435 (M + H) 19.32hydroxyimidazo[4,5-e]pyrazin-6- yl]ethynyl}imidazo[4,5-b]pyrazin-2-ol6-(dimethylamino)-1-(ethylpropyl)imidazo[4,5- 250 (M + H) 2.79b]pyrazin-2-ol 6-ethyl-1-(ethylpropyl)imidazo[4,5-b]pyrazin-2-ol 235[M + H] 8.58 ^(†)Mean value. ^(‡)Median value.

Using procedures similar to those described herein, the compounds in thefollowing table were also synthesized and tested.

Name(S)-1-(2-hydroxy-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-6-yl)ethanone(S)-6-acetyl-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one(S)-6-isobutyl-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol(S)-6-isobutyl-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one(S)-6-hexyl-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol(S)-6-hexyl-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one(S)-6-cyclohexyl-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol(S)-6-cyclohexyl-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one(S)-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol(S)-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one(S)-2-hydroxy-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazine-6-carboxylicacid(S)-2-oxo-3-(1-phenylethyl)-2,3-dihydro-1H-imidazo[4,5-b]pyrazine-5-carboxylicacid (S)-methyl2-hydroxy-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazine-6-carboxylate(S)-methyl2-oxo-3-(1-phenylethyl)-2,3-dihydro-1H-imidazo[4,5-b]pyrazine-5-carboxylate(S)-2-hydroxy-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazine-6-carbonitrile(S)-2-oxo-3-(1-phenylethyl)-2,3-dihydro-1H-imidazo[4,5-b]pyrazine-5-carbonitrile(S)-2-hydroxy-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazine-6-carboxamide(S)-2-oxo-3-(1-phenylethyl)-2,3-dihydro-1H-imidazo[4,5-b]pyrazine-5-carboxamide(S)-2-hydroxy-N-methyl-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazine-6-carboxamide(S)-N-methyl-2-oxo-3-(1-phenylethyl)-2,3-dihydro-1H-imidazo[4,5-b]pyrazine-5-carboxamide(S)-2-hydroxy-N,N-dimethyl-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazine-6-carboxamide(S)-N,N-dimethyl-2-oxo-3-(1-phenylethyl)-2,3-dihydro-1H-imidazo[4,5-b]pyrazine-5-carboxamide(S)-N,N-diethyl-2-hydroxy-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazine-6-carboxamide(S)-N,N-diethyl-2-oxo-3-(1-phenylethyl)-2,3-dihydro-1H-imidazo[4,5-b]pyrazine-5-carboxamide(S)-(2-hydroxy-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-6-yl)(morpholino)methanone(S)-6-(morpholine-4-carbonyl)-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one(S)-(2-hydroxy-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-6-yl)(piperidin-1-yl)methanone(S)-1-(1-phenylethyl)-6-(piperidine-1-carbonyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one(S)-(2-hydroxy-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-6-yl)(4-methylpiperazin-1-yl)methanone(S)-6-(4-methylpiperazine-1-carbonyl)-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one(S)-N-benzyl-2-hydroxy-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazine-6-carboxamide(S)-N-benzyl-2-oxo-3-(1-phenylethyl)-2,3-dihydro-1H-imidazo[4,5-b]pyrazine-5-carboxamide(S)-6-((dimethylamino)methyl)-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol(S)-6-((dimethylamino)methyl)-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one(S)-6-(morpholinomethyl)-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol(S)-6-(morpholinomethyl)-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one(S)-1-(1-phenylethyl)-6-(piperidin-1-ylmethyl)-1H-imidazo[4,5-b]pyrazin-2-ol(S)-1-(1-phenylethyl)-6-(piperidin-1-ylmethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one(S)-6-((4-methylpiperazin-1-yl)methyl)-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol(S)-6-((4-methylpiperazin-1-yl)methyl)-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one(S)-6-(2-hydroxypropan-2-yl)-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol(S)-6-(2-hydroxypropan-2-yl)-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one6-(methylsulfinyl)-1-((S)-1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol6-(methylsulfinyl)-1-((S)-1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one(S)-6-(methylsulfonyl)-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2-ol(S)-6-(methylsulfonyl)-1-(1-phenylethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one6-cyclopropyl-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2-ol6-cyclopropyl-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one6-bromo-1-(tetrahydro-2H-pyran-4-yl)-1H-imidazo[4,5-b]pyrazin-2-ol6-bromo-1-(tetrahydro-2H-pyran-4-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one1-cyclopropyl-6-(methylthio)-1H-imidazo[4,5-b]pyrazin-2-ol1-cyclopropyl-6-(methylthio)-1H-imidazo[4,5-b]pyrazin-2(3H)-one6-(methylthio)-1-(tetrahydro-2H-pyran-4-yl)-1H-imidazo[4,5-b]pyrazin-2-ol6-(methylthio)-1-(tetrahydro-2H-pyran-4-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one(E)-1-cyclopropyl-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2-ol(E)-1-cyclopropyl-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one(E)-6-(prop-1-enyl)-1-(tetrahydro-2H-pyran-4-yl)-1H-imidazo[4,5-b]pyrazin-2-ol(E)-6-(prop-1-enyl)-1-(tetrahydro-2H-pyran-4-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one(Z)-1-cyclopropyl-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2-ol(Z)-1-cyclopropyl-6-(prop-1-enyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one(Z)-6-(prop-1-enyl)-1-(tetrahydro-2H-pyran-4-yl)-1H-imidazo[4,5-b]pyrazin-2-ol(Z)-6-(prop-1-enyl)-1-(tetrahydro-2H-pyran-4-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one6-bromo-1-cyclopropyl-1H-imidazo[4,5-b]pyrazin-2-ol6-bromo-1-cyclopropyl-1H-imidazo[4,5-b]pyrazin-2(3H)-one5-(methylthio)-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2-ol5-(methylthio)-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one5-ethyl-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2-ol5-ethyl-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one1-(pentan-3-yl)-5-vinyl-1H-imidazo[4,5-b]pyrazin-2-ol1-(pentan-3-yl)-5-vinyl-1H-imidazo[4,5-b]pyrazin-2(3H)-one methyl2-hydroxy-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazine-5-carboxylate methyl2-oxo-1-(pentan-3-yl)-2,3-dihydro-1H-imidazo[4,5-b]pyrazine-5-carboxylate2-hydroxy-N,N-dimethyl-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazine-5-carboxamideN,N-dimethyl-2-oxo-1-(pentan-3-yl)-2,3-dihydro-1H-imidazo[4,5-b]pyrazine-5-carboxamide2-hydroxy-N-methyl-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazine-5-carboxamideN-methyl-2-oxo-1-(pentan-3-yl)-2,3-dihydro-1H-imidazo[4,5-b]pyrazine-5-carboxamide1-(2-hydroxy-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-5-yl)ethanone5-acetyl-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one(S)-1-(1-phenylethyl)-1H-imidazo[4,5-b]quinoxalin-2-ol(S)-1-(1-phenylethyl)-1H-imidazo[4,5-b]quinoxalin-2(3H)-one2-(6-bromo-2-hydroxy-1H-imidazo[4,5-b]pyrazin-1-yl)propane-1,3-diol6-bromo-1-(1,3-dihydroxypropan-2-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one6-bromo-1-(2-morpholinoethyl)-1H-imidazo[4,5-b]pyrazin-2-ol6-bromo-1-(2-morpholinoethyl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one2-hydroxy-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazine-5-carboxylic acid2-oxo-1-(pentan-3-yl)-2,3-dihydro-1H-imidazo[4,5-b]pyrazine-5-carboxylicacid

Example 12 Rodent Model of Experimental Autoimmune Myasthenia Gravis(EAMG)

A rodent model of myasthenia gravis was developed based on a modeldescribed by V. A. Lennon et al. (J. Exp. Med., 141: 1365-1375, 1975).Female Sprague-Dawley rats (200-300 g) were purchased from Charles RiverLaboratories and given a minimum 72 hours acclimation period.Experimental autoimmune Myasthenia Gravis (EAMG) was induced by a singleintra-peritoneal injection of 500 μg/kg of AChRα1/3/5 antibody(SC-58604, Santa Cruz Biotechnology, CA, USA). Fore- and hind-limb gripmeasurements were acquired in triplicate with a 5 kg Dual Sensor GripMeter (Columbus Instruments, Ohio, USA). The rats were lowered onto atriangle bar of the grip strength meter until the animals gripped thebar with their forelimbs, and then the rats were pulled gently backwarduntil their grip broke. The rats were then moved toward the T bar untiltheir hind legs gripped and pulled back gently until their grip broke.The force gauge of the grip meter recorded the maximum force. Baselinebody weight and fore- and hind-grip strength of animals was measuredprior to inducing EAMG. Animals were monitored for changes in bodyweight for 96 hours. Grip strength was assessed at 24, 48, 72 and 96hours following injection of AChRα1/3/5 antibody (in triplicate).

As shown in FIGS. 1A and 1B, the antibody-treated animals demonstratedweight loss (FIG. 1A) and decreased forelimb grip strength (FIG. 1B) ascompared to control animals.

Example 13 Validation of EAMG Model

Female Sprague-Dawley rats (200-300 g) were purchased from Charles RiverLaboratories and given a minimum 72 hours acclimation period.Experimental autoimmune Myasthenia Gravis (EAMG) was induced by a singleintra-peritoneal injection of 500 μg/kg of AChRα1/3/5 antibody(SC-58604, Santa Cruz Biotechnology, CA, USA). Fore- and hind-limb gripmeasurements were acquired in triplicate with a 5 kg Dual Sensor GripMeter (Columbus Instruments, Ohio, USA) as described in Example 1.Baseline body weight and fore- and hind-grip strength of animals wasmeasured before inducing EAMG. 72 hours after antibody injection, ratswere reassessed for body weight and grip strength (in triplicate) andrats that showed a 40 to 70 percent drop from baseline were included inthe study.

Selected rats were divided into vehicle and compound treated groups.Neostigmine (an acetylcholinesterase inhibitor that is used clinicallyfor the assessment and treatment of myasthenia gravis) was administeredto test animals intraperitoneally at 0.2 mg/kg. After dosing, rats werereassessed for grip strength at 5, 10 and 20 minutes. As shown in FIG.2, neostigmine increased forelimb grip strength of test animals 5minutes after treatment.

Example 14 Effect of Test Compound on Grip Strength of Control Animals

Female Sprague-Dawley rats (200-300 g) were purchased from Charles RiverLaboratories and given a minimum 72 h acclimation period. Fore- andhind-limb grip measurements were acquired in triplicate with a 5 kg DualSensor Grip Meter (Columbus Instruments, Ohio, USA) as described inExample 1. Rats were weighed and divided into vehicle and compoundtreated groups. The compound of Example 4(6-ethynyl-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2-ol) was formulatedas a suspension in 0.5% HPMC & 0.2% Tween-80 and administered orally at20 mg/kg with a dosing volume of 5 mL/kg. After dosing, rats werereassessed for grip strength at 30 and 60 minutes. Grip strengthmeasurements were normalized to animal body weight and expressed as apercent change from the baseline grip.

As shown in FIGS. 3A and 3B, the test compound had no effect on forelimbgrip strength of control rats.

Example 15 Effect of Test Compound on Grip Strength of EAMG Animals

Female Sprague-Dawley rats (200-300 g) were purchased from Charles RiverLaboratories and given a minimum 72 hours acclimation period.Experimental autoimmune Myasthenia Gravis (EAMG) was induced by a singleintra-peritoneal injection of 500 μg/kg of AChRα1/3/5 antibody(SC-58604, Santa Cruz Biotechnology, CA, USA). Fore- and hind-limb gripmeasurements were acquired in triplicate with a 5 kg Dual Sensor GripMeter (Columbus Instruments, Ohio, USA) as described in Example 1.Baseline body weight and fore- and hind-grip strength of animals wasmeasured before inducing EAMG. Animals were monitored daily for changesin body weight for 96 hours. 72 hours after antibody injection, ratswere reassessed for body weight and grip strength (in triplicate) andrats that showed a 40 to 70 percent drop from baseline were included inthe study.

Selected rats were divided into vehicle and compound treated groups. Thecompound of Example 4(6-ethynyl-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2-ol) was formulatedas a suspension in 0.5% HPMC & 0.2% Tween-80 and administered orally at5, 10 & 20 mg/kg with a dosing volume of 5 mL/kg. After dosing, ratswere reassessed for grip strength at 30 and 60 minutes. 96 hours afterantibody injection, the efficacy of the test compound was reexamined ina crossover design with the rats. Grip strength measurements werenormalized to animal body weight and expressed as a percent change fromthe baseline grip. Statistical significance was calculated by thedifferences in the least square mean between vehicle and treated groupand P<0.05 was considered significance.

As shown in FIGS. 4A and 4B, the test compound improved the forelimbgrip strength in test animals in a dose-dependent manner at 30 and 60minutes after dosing. Table 1 summarizes the observed percentimprovement in forelimb grip strength for each dose at each timepoint.

TABLE 1 30 Min. 60 Min.  5 mg/kg 15 19 10 mg/kg 28 26 20 mg/kg 33 42

Example 16 In-Situ Muscle Model

D-tubocurarine, a non-depolarizing neuromuscular blocker and competitiveacetylcholine receptor inhibitor, was used to simulate competitiveinhibition of neuromuscular junction signaling in an in-situ musclemodel.

Male Sprague-Dawley rats (275-400 g) were anesthetized under isofluraneanesthesia and the skin around the experimental leg was cut opened. Thedistal end of the extensor digitorum longus (EDL) muscle and itsassociated tendon were then isolated. The rat was then placed on theplatform of an Aurora in-situ muscle analysis rig (806C) maintained atbody temperature via a circulating water system. The knee wasimmobilized in a clamp between two sharpened screws and the distaltendon cut and tied to the arm of a force transducer (Aurora Scientific,Ontario, Canada) using a silk suture. The muscle was stimulated directlyvia the peroneal nerve. For isolation of the nerve, a 1 cm incision wasmade at the upper thigh and the overlying gastrocnemius muscle was cutto expose an approximate 5 mm stretch of the peroneal nerve. This wasthen dissected free of surrounding connective tissue and a pair ofstainless steel needle electrodes (0.10 mm) were hooked around theexposed nerve. Muscle contractile properties were assessed by applyingan electrical current to the nerve and recording the force generated bythe muscle via a servomotor. The muscle length was adjusted to producethe maximum isometric force (L_(o)) after sub-maximal stimulation (30Hz, 1 ms pulses, 350 ms train duration). Once L_(o) had beenestablished, the nerve was stimulated every 2 minutes with a 30 Hz train(1 ms stimuli, 350 ms duration) for the course of the experiment. Thispreparation was stable for 4-6 hours.

After stabilization, d-tubocurarine was infused at a rate of 75 ug/kg/hrintravenously and the muscle contraction was continuously monitored. Theinfusion rate was adjusted to maintain a 70% of the baselinecontraction. Once the decreased contraction was stabilized, rats wereadministered either saline or the compound of Example 4 (10 mg/kg or 20mg/kg, ID) and the change in the contraction was monitored over 90minutes. Data was expressed as a percent force change from baseline(i.e., pre-d-tubocurarine injection contraction).

Referring to FIG. 5, continuous infusion of d-tubocurarine caused areduction in the force of contraction of EDL muscle, whereasadministration of the compound of Example 4 caused a dose-dependentincrease in the force of contraction of EDL muscle in the presence ofd-tubocurarine. These data suggest that, by sensitizating skeletalmuscle to stimulation, the compounds described herein may improve musclestrength and help counteract decreases in neural drive observed inmyasthenia gravis patients.

While some embodiments have been shown and described, variousmodifications and substitutions may be made thereto without departingfrom the spirit and scope of the invention. For example, for claimconstruction purposes, it is not intended that the claims set forthhereinafter be construed in any way narrower than the literal languagethereof, and it is thus not intended that exemplary embodiments from thespecification be read into the claims. Accordingly, it is to beunderstood that the present invention has been described by way ofillustration and not limitations on the scope of the claims.

What is claimed is:
 1. A compound of Formula I

wherein R₁ is ethynyl, R₂ is pentan-3-yl, and R₄ is hydrogen, or apharmaceutically acceptable salt thereof.
 2. A pharmaceuticallyacceptable composition comprising a pharmaceutically acceptable carrierand a compound of claim 1, or a pharmaceutically acceptable saltthereof.
 3. A method for treating myasthenia gravis in a patient,comprising administering to the patient, an effective amount of acompound of claim 1, or a pharmaceutically acceptable salt thereof.
 4. Amethod for treating amyotrophic lateral sclerosis in a patient,comprising administering to the patient, an effective amount of acompound of claim 1, or a pharmaceutically acceptable salt thereof.
 5. Amethod for treating myasthenia gravis in a patient, comprisingadministering to the patient, an effective amount of a composition ofclaim
 2. 6. A method for treating amyotrophic lateral sclerosis in apatient, comprising administering to the patient, an effective amount ofa composition of claim
 2. 7. A compound of Formula II

wherein R₁ is ethynyl, R₂ is pentan-3-yl, and R₄ is hydrogen, or apharmaceutically acceptable salt thereof.
 8. A pharmaceuticallyacceptable composition comprising a pharmaceutically acceptable carrierand a compound of claim 7, or a pharmaceutically acceptable saltthereof.
 9. A method for treating myasthenia gravis in a patient,comprising administering to the patient, an effective amount of acompound of claim 7, or a pharmaceutically acceptable salt thereof. 10.A method for treating amyotrophic lateral sclerosis in a patient,comprising administering to the patient, an effective amount of acompound of claim 7, or a pharmaceutically acceptable salt thereof. 11.A method for treating myasthenia gravis in a patient, comprisingadministering to the patient, an effective amount of a composition ofclaim
 8. 12. A method for treating amyotrophic lateral sclerosis in apatient, comprising administering to the patient, an effective amount ofa composition of claim
 8. 13. A pharmaceutically acceptable compositioncomprising: a pharmaceutically acceptable carrier,6-ethynyl-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2-ol or apharmaceutically acceptable salt thereof, and6-ethynyl-1-(pentan-3-yl)-1H-imidazo[4,5-b]pyrazin-2(3H)-one or apharmaceutically acceptable salt thereof.